Single channel lower part for a pipette and pipette with an upper part and a single channel lower part

Abstract

A single-channel lower part for a pipette comprising a hollow cylindrical housing lower part with an interior, an opening at the upper end, a housing base at the lower end, a projection for attaching a pipette tip, which projects downwards from the housing base and has a through-channel extending from the lower end of the projection into the interior, and a spring chamber forming the interior or part thereof, having the opening at the top and at least one radially inwardly projecting boundary with a through-opening at the bottom, a rod-shaped piston actuator for displacing a piston in a cylinder, wherein the piston actuator is arranged at least partially in the spring chamber, extends in the axial direction of the hollow cylindrical housing lower part and is directed towards the through-opening, a contact surface for a push rod of a drive device arranged at the upper end of the piston actuator, and a spring support.which is connected to the piston actuator above the limit and projects radially outwards from it, a helical spring arranged in the spring chamber, supported at the top on the underside of the spring support and at the bottom on the limit and through which the piston actuator extends, a first guide for guiding the piston actuator in the axial direction of the hollow cylindrical housing lower part, which has at least a first guide surface on the inner circumference of the spring chamber and at least a second guide surface on the outer circumference of a guide element projecting radially outwards from the piston actuator and connected to it.

Description

[0001] The invention relates to a single-channel lower part for a pipette and a pipette with a top part and a single-channel lower part.

[0002] Pipettes are used primarily in scientific and industrial laboratories with medical, molecular biological, and pharmaceutical applications for dispensing specific volumes of liquids. These liquids can be homogeneous (single-phase) liquids consisting of a single liquid component or a homogeneous mixture of several liquid components (solutions). Furthermore, the liquids can be heterogeneous (multi-phase) mixtures of a liquid with another liquid (emulsion) or a solid (suspension).

[0003] Common pipettes have a body shaped like an elongated hollow cylinder with a prong (connection) at the bottom for attaching a pipette tip. The prong is often a conical, cylindrical, or partially conical and cylindrical projection, also known as the "working cone." A pipette tip is a hollow tube with a tip opening at the bottom and a fitting opening at the top, allowing the tip to be attached to the prong. The liquid is drawn into and dispensed from the pipette tip. The aspiration and dispensing of the liquid are controlled by the pipette. Fixed-volume pipettes are used for pipetting constant volumes. With variable-volume pipettes, the volume to be dispensed can be set. A mechanical counter displays the set volume.To adjust the volume, the stroke of a drive unit is set using an adjustment mechanism coupled to the counter. After use, the pipette tip is detached from the base and can be replaced with a fresh one. This prevents cross-contamination during subsequent pipetting operations.

[0004] Air-cushion pipettes have a piston-cylinder or other displacement mechanism within the pipette body, connected via a passage to a hole at the bottom of the stem. Moving the piston within the cylinder by means of the drive mechanism moves a cushion of air, drawing liquid into and expelling it from a pipette tip clamped onto the stem. Single-use or reusable pipette tips are typically made of plastic.

[0005] Air-cushion pipettes can become contaminated with the displacement mechanism. This can be due to the ingress of liquid into the displacement mechanism as a result of improper handling, or of vapors or minute droplets of the liquid being pipetted.

[0006] Positive displacement pipettes are used with pipette tips featuring an integrated piston. This type of pipette has a pin for attaching the pipette tip and a drive mechanism that can be coupled to the integrated piston (tip piston) to move the piston. The piston comes into direct contact with the liquid, thus eliminating the adverse effects of an air cushion. Positive displacement pipettes are particularly suitable for dispensing liquids with high vapor pressure, high viscosity, or high density, and for applications in molecular biology where aerosol-free dispensing is essential to prevent contamination.

[0007] Air cushion pipettes are already known in which a lower part with the displacement device and the attachment point for the pipette tip can be separated from an upper part with a drive unit for powering the displacement device. This facilitates the assembly and disassembly of the displacement device and drive unit, as well as cleaning, maintenance, and repair, and allows the same upper part to be used for connection with different single-channel and / or multi-channel lower parts.

[0008] EP 1 559 480 B1 describes a pipette in which the displacement device and the drive device can be connected and disconnected more easily and quickly. The pipette has a displacement device with a displacement chamber having a movable boundary, which, according to a preferred embodiment, is hereinafter referred to as a piston. Furthermore, the pipette has a projection for connecting to a pipette tip and a connecting channel between the displacement chamber and the free end of the projection. In addition, the pipette has a drive device for actuating the piston of the displacement device with a drive element that has a detachable operative connection to the piston.Furthermore, it has a bayonet connection between the drive unit and the displacement unit, which can be established by creating the functional connection between the drive unit and the piston and can be detached by releasing the functional connection between the drive unit and the piston.

[0009] The actuating element is a pushrod of the actuating device that can be displaced parallel to the longitudinal axis of the bayonet connection. The displacement device has a contact surface, connected to the piston via a piston rod and oriented transversely to the pushrod, which is pressed against the lower end of the pushrod by a rebound spring. The rebound spring is a coil spring that surrounds the piston rod. The operative connection between the actuating element and the piston is established by engaging the bayonet connection and released by disengaging the bayonet connection.

[0010] Based on this, the invention aims to provide a single-channel lower part for a pipette that enables safer and more accurate pipetting.

[0011] The problem is solved by a single-channel lower part for a pipette according to claim 1. Advantageous embodiments of the invention are specified in the dependent claims and in the following description.

[0012] The single-channel lower part for a pipette according to the invention comprises: a hollow cylindrical housing lower part with: ∘ an interior space, ∘ an opening at the upper end, ∘ a housing base at the lower end, ∘ a projection for attaching a pipette tip, which projects downwards from the housing base and has a through-channel extending from the lower end of the projection into the interior space, and ∘ a spring chamber forming the interior space or part thereof, having the opening at the top and at least one radially inwardly projecting boundary with a through-opening at the bottom, a rod-shaped piston actuator for displacing a piston in a cylinder, wherein the piston actuator is arranged at least partially in the spring chamber, extends in the axial direction of the hollow cylindrical housing lower part and is aligned with the through-opening, a contact surface for a push rod of a drive device arranged at the upper end of the piston actuator, a spring support,a helical spring arranged in the spring chamber, supported at the top on the underside of the spring support and at the bottom on the limit, through which the piston actuator extends, a first guide for guiding the piston actuator in the axial direction of the hollow cylindrical housing lower part, which has at least one first guide surface on the inner circumference of the spring chamber and at least one second guide surface on the outer circumference of a guide element projecting radially outwards from and connected to the piston actuator.

[0013] The applicant has determined that, particularly in large-volume pipettes designed for use with pipette tips of nominal volumes of 2 ml, 5 ml, or 10 ml, the piston of the displacement device can tilt within the cylinder under unfavorable circumstances. This can occur, for example, when the lower part and the displacement device located therein are coupled to the upper part and the drive mechanism located therein of an air cushion pipette. According to the applicant's findings, tilting the piston can create a gap between the seal and the cylinder wall, resulting in slight to significant leakage between the piston and the cylinder. This can distort the pipetting results or even make pipetting impossible. Furthermore, tilting the piston within the cylinder can increase wear and tear and the need for repairs.

[0014] According to the invention, the detrimental tilting of the piston in the cylinder is prevented by aligning the piston actuator, used to move the piston within the cylinder, in the spring chamber of the lower housing. Thus, the piston is not only guided in the cylinder but also aligned at a distance from the cylinder within the spring chamber by means of the piston actuator. Consequently, tilting of the piston in the cylinder, with its associated disadvantages, is avoided. This increases the accuracy of pipetting, reduces pipette wear, and decreases the effort required for calibration and repair. The expansion of the guide surfaces, the friction occurring during piston movement, and the manufacturing effort for the guide surfaces can all be minimized.

[0015] The advantageous effects of the invention are particularly pronounced in large-volume pipettes with a nominal volume of at least 2 ml, since the pistons of large-volume pipettes, due to their large cross-section, are especially prone to tipping. However, the advantageous effects of the invention can also be utilized for pipettes with a smaller nominal volume. The invention can be used with both air-cushion pipettes and positive displacement pipettes. It is suitable for use with fixed-volume pipettes and variable-volume pipettes. The invention is particularly suitable for manually operated and electrically operated pipettes, preferably for hand-held pipettes that can be held and operated with only one hand. The invention can also be advantageously used for automated laboratory systems and dosing systems that utilize the single-channel lower section according to claim 1.

[0016] According to one embodiment of the invention, the contact surface is the top of the piston actuator and / or the top of the spring support. This integrates the contact surface into existing components of the design and reduces construction effort.

[0017] According to another embodiment, the contact surface is the upper surface of a piston head connected to the upper end of the piston actuator, which has a larger cross-section than the adjacent area of ​​the piston actuator. This provides a particularly large contact area, which can facilitate connecting the lower housing part to the upper housing part and centering the lower end of a push rod on the contact surface. According to yet another embodiment, the piston head is detachably attached to the upper end of the piston actuator or integrally connected to the upper end of the piston actuator.

[0018] According to another embodiment, the contact surface is dome-shaped. The dome-shaped contact surface allows a lifting rod placed on it with its lower end to be centered, thereby preventing lateral forces acting on the piston actuator that would cause increased friction in the first guide.

[0019] In another embodiment, the spring support comprises a spring seat held on the piston actuator and a spring retainer that secures the spring seat to the piston actuator. This simplifies the assembly of the piston actuator, spring seat, and spring retainer. In another embodiment, the spring retainer is detachably attached to the piston actuator. This allows for disassembly, for example, for maintenance or repair. In yet another embodiment, the spring seat and the spring retainer are separate components. Alternatively, the spring seat and the spring retainer are formed as a single piece. Using single-piece components reduces manufacturing and assembly costs. In yet another embodiment, the spring retainer is a component of the lower part whose sole function is to secure the spring seat to the piston actuator.According to another embodiment, the contact surface is formed on the upper side of the spring retainer. As a result, a particularly large contact surface can be provided, which can facilitate the assembly of the lower part to the upper part and the centering of the lower end of a lifting rod.

[0020] According to another embodiment, the guide element is the piston head and / or the spring support. This allows the first guide to be positioned at a particularly large distance from the cylinder, resulting in especially good piston alignment. Furthermore, it reduces construction effort. According to yet another embodiment, the piston head and / or the spring support has the second guide surface on its outer circumference.

[0021] According to another embodiment, the first guide surface and the second guide surface are circular cylinders. This is particularly advantageous for the simple and precise manufacturing of the guide surfaces.

[0022] According to another embodiment, the spring chamber has two diametrically opposed, each only partially circumferential, first guide surfaces distributed symmetrically around its central axis. The guide element rests against these surfaces with a single fully circumferential second guide surface or with two diametrically opposed, each only partially circumferential, second guide surfaces distributed symmetrically around the piston actuator. This enables particularly low-friction and uniform guidance of the piston actuator.

[0023] According to an alternative embodiment, the spring chamber has only a single, fully circumferential first guide surface, against which the guide element rests with symmetrically distributed, preferably two diametrically opposed, second guide surfaces, each only partially circumferential, arranged around the piston actuator. This enables particularly low-friction and uniform guidance of the piston actuator.

[0024] According to another embodiment, the guide element has a hollow cylindrical section and at least one second guide surface on the outer circumference of the hollow cylindrical section, with the hollow cylindrical central section accommodating the upper end of the piston rod. This allows for a structurally simple design of the guide element, which is easy to assemble and, if necessary, disassemble.

[0025] According to another embodiment, the second guide surfaces are located on the outside of the wings, projecting outwards from the circumference of the hollow cylindrical section. This allows for a structurally simple design of the guide element, which exhibits elastic deformability, thereby reducing frictional forces.

[0026] According to one embodiment, the wings have cavities with a circular arc cross-section running parallel to the piston actuator. This prevents material accumulation, which is particularly advantageous for dimensionally accurate injection molding of the plastic guide element. Furthermore, the circular arc cross-section increases elasticity.

[0027] According to one embodiment, the guide element has at least one knurling on its outer circumference, preferably two diametrically opposed knurling patterns. The knurling facilitates the assembly and, if necessary, the disassembly of the guide element.

[0028] According to another embodiment, the guide element has a snap connection and / or a positive-locking connection and / or a press-fit connection and / or a connection to the piston actuator via another component. This facilitates the assembly and, if necessary, the disassembly of the guide element. For disassembly purposes, the snap connection and / or the positive-locking connection and / or the press-fit connection and / or the connection via another component is designed as a detachable connection.

[0029] According to another embodiment, the guide element and the piston actuator each have at least one connecting element configured to form a snap-fit ​​connection and / or a positive-locking connection and / or a press fit. According to another embodiment, the at least one connecting element of the guide element is integrally connected to the guide element, and the at least one connecting element of the piston actuator is integrally connected to the piston actuator. According to another embodiment, the additional component is a component of the lower part whose sole function is to fasten the guide element to the piston actuator. According to another embodiment, the hollow cylindrical section has at least one connecting element on its inner circumference that is connected to the piston actuator.According to another embodiment, the hollow cylindrical section and the piston actuator have matched connecting elements that are connected to each other. According to another embodiment, the matched connecting elements are elements of a snap-fit ​​connection and / or a positive-locking connection and / or a press fit. According to another embodiment, the hollow cylindrical section has four inwardly projecting, parallel legs on its inner circumference, the ends of which engage in a groove on the circumference of the piston actuator.

[0030] According to another design, the boundary is a step that runs completely or partially around the inner circumference of the interior space at the lower end of the spring chamber.

[0031] According to another embodiment, the pipette is an air cushion pipette. According to another embodiment, the lower housing part has a hollow cylindrical upper housing section that includes the spring chamber, which forms part of the interior, and the lower housing part has a hollow cylindrical lower housing section that includes a receiving chamber, which is bounded at the bottom by the housing base and forms another part of the interior. A cylinder is arranged in the receiving chamber, the cylinder is connected at the bottom to the through-channel of the nozzle, a piston is arranged in the cylinder, the piston seals against the inside of the cylinder at its circumference, and the piston is displaceable in the axial direction of the cylinder. A piston actuator in the form of a piston rod is connected to the piston, extending upwards from the piston through the through-opening into the upper housing section.In this air cushion pipette, the piston, which is guided in the cylinder located in the receiving chamber, is additionally aligned by the first guide of the piston actuator, thus preventing the piston from tilting.

[0032] According to another embodiment, the receiving chamber of the lower housing section has a larger diameter than the spring chamber of the upper housing section. This allows for a receiving chamber for a cylinder with a piston that can be moved within it, with a predetermined stroke and volume, to be provided with relatively little structural effort.

[0033] In another embodiment, a connecting section joins the lower edge of the upper housing section to the upper edge of the lower housing section. This connecting section can bridge different diameters between the upper and lower housing sections. By connecting upper and lower housing sections with different diameters using this connecting section, the overall construction effort can be kept relatively low.

[0034] In another embodiment, the connecting section comprises an annular cover and a hollow cylindrical rim projecting downwards from the outer edge of the cover. The upper housing section is connected to the top of the cover, the rim is connected to the upper edge of the lower housing section, and the cover completely covers the receiving chamber. The connecting section simultaneously forms a cover for the receiving chamber and the cylinder located therein. The cover can be manufactured integrally with the upper housing section. This is advantageous for manufacturing the upper and lower housing sections by injection molding, as undercuts can be avoided. After injection molding, the upper housing section can be joined at the rim of the cover, and the upper edge of the lower housing section can be joined together.

[0035] In another embodiment, the enclosing element is connected to the upper edge of the lower housing section via a screw connection, a bayonet connection, a detachable snap connection, or another detachable connection. This makes it possible to open the lower housing section non-destructively for cleaning, maintenance, or repair purposes and then close it again, for example, to replace a piston seal in the cylinder.

[0036] Alternatively, the edging is connected to the upper edge of the lower housing section via a non-removable connection, for example by a snap connection that cannot be removed without damage, by hot melting or by gluing.

[0037] According to another design, the pipette is a positive displacement pipette. Even with positive displacement pipettes, it can be advantageous to assemble them from a lower and a upper part to facilitate assembly, disassembly, cleaning, maintenance, and repair, and to allow the same upper part to be used for connection with different single-channel and / or multi-channel lower parts.

[0038] According to another embodiment, the piston actuator has a device at its lower end for connecting to the upper end of a tip piston inserted into a pipette tip that can be clamped onto the base. In this embodiment, the piston actuator is designed to connect to the tip piston of a pipette tip with an integrated tip piston, which can be clamped onto the base. The alignment of the piston actuator with the first guide prevents the tip piston from tilting within the pipette tip.

[0039] According to another embodiment, a second guide for the piston actuator is provided in the axial direction of the hollow cylindrical housing lower part, which has at least a third guide surface at the through-hole and at least a fourth guide surface on the circumference of the piston actuator. This second guide further improves the alignment of the piston in the cylinder and counteracts tilting.

[0040] In one embodiment, the through-opening in the boundary has a circular cross-section. In another embodiment, the through-opening has two diametrically opposed guide grooves, and the piston rod has at least two diametrically opposed, outwardly projecting guide ribs on its outer circumference that engage in the guide grooves. The guidance of the guide ribs in the guide grooves provides anti-rotation protection. This ensures the alignment of the first and second guide surfaces of the first guide with each other and thus the desired alignment of the piston.

[0041] According to another embodiment, the cylinder has a volume of at least 2 ml, preferably 2, 5, or 10 ml. The improvement in dosing accuracy and the prevention of damage are particularly significant for large-volume pipettes with a nominal volume in the aforementioned range or with the stated values.

[0042] Furthermore, the invention relates to a pipette comprising an upper part and a single-channel lower part according to one of claims 1 to 24 or one of the embodiments specified in the description, wherein the upper part comprises a housing upper part, an operating button on the outside of the housing upper part, a drive unit arranged in the housing upper part and operatively connected to the operating button, and a movable stroke rod of the drive unit, the lower end of which is accessible from the outside at a further opening of the housing upper part, wherein the upper part and the single-channel lower part are designed to be brought into a connected position in which the lower end of the stroke rod contacts the contact surface of the piston actuator and a connecting device is provided which connects the upper part and the lower part to each other in the connected position.

[0043] The invention is explained in more detail below with reference to the accompanying drawings of an exemplary embodiment. The drawings show: Fig. 1 a manually driven air cushion pipette with the single-channel lower part according to the invention in a vertical section; Fig. 2 the same lower part in an enlarged vertical section; Fig. 3 the same lower part in a top view; Fig. 4 the same lower part in a horizontal sectional view from above;

[0044] Fig.5a-e Piston actuator with spring support before assembly in a perspective view from an oblique angle above ( Fig. 5a ) and from below ( Fig. 5b ), in its pre-assembled state in a perspective view from an angle above ( Fig. 5c ) and in a top view ( Fig. 5d ) and in the assembled state in a top view ( Fig. 5e ).

[0045] In the present application, the terms "top" and "bottom", "above" and "below", and derived terms such as "bottom" and "top", and "horizontal" and "vertical" refer to an orientation of the pipette in which the seat is located at the bottom of the pipette and is oriented vertically downwards. In this orientation, a pipette tip mounted on the seat can be directed towards a vessel below in order to aspirate liquid into the pipette tip and dispense it from the pipette tip.

[0046] According to Fig. 1 A pipette 1 has a rod-shaped housing 2 with a hollow cylindrical housing lower part 3 and a housing upper part 4 in the form of an elongated hollow body.

[0047] According to Fig. 2 bis 5 The lower housing section 3 has a hollow cylindrical upper housing section 5, which includes a spring chamber 6, and a hollow cylindrical lower housing section 7, which includes a receiving chamber 8. The spring chamber 6 and the receiving chamber 8 together form an interior space 9 of the lower housing section 3. The lower housing section 7 has a larger inner diameter than the upper housing section 5.

[0048] The upper housing section 5 has a circular cylindrical upper side wall 10 that laterally delimits the spring chamber 6. The upper housing section 5 has a circular opening 11 at the top, bounded by the upper edge of the upper side wall 10, leading into the spring chamber 6, and a radially inwardly projecting boundary 12 at the bottom in the form of a shoulder 13 circumferentially around the inner circumference of the upper side wall, which delimits the spring chamber 6 at the bottom. A circular through-opening 14 is formed centrally in the shoulder 13. The through-opening 14 has two diametrically opposed, axially extending guide grooves 15 on its inner circumference.

[0049] The upper side wall 10 has two inwardly projecting, base-like areas 16 on its inner circumference, which extend axially along the spring space 6 and circumferentially only over a portion of the inner circumference and are diametrically opposed to each other. The base-like areas 16 lie in front of and behind the plane of the drawing. Fig.1 and 2 and are in Fig.3 shown. The base-shaped areas 16 each form with their inner side a first circular cylindrical guide surface 17 with a radius of curvature around the central axis of the spring space 6.

[0050] The lower housing section 7 has a circular cylindrical lower side wall 18 that laterally delimits the receiving chamber 8. At the top, the lower housing section 7 has a further opening 19. At the bottom, the lower housing section 7 has a conical base 20 that delimits the receiving chamber 8 at the bottom. A slender, tubular, slightly conical projection 21 extends downwards from the base 20, featuring a seat 22 with a circumferential groove for an O-ring to secure a pipette tip 23. The projection 21 has a circular channel 24 extending from the lower end of the projection into the receiving chamber 8.

[0051] The upper housing section 5 is connected to the lower housing section 7 via a connecting section 25. The connecting section 25 has an annular cover 26, which is integrally connected to the lower edge of the upper side wall 10. A downwardly projecting, circular cylindrical recess 27 of the connecting section 25 is integrally connected to the outer edge of the cover 26. The recess 27 has an internal thread 28, and the lower side wall 18 has an external thread 29 at its upper edge that matches the internal thread 28. The internal thread 28 of the connecting section 25 is screwed into the external thread 29 of the lower side wall 18, thereby connecting the upper housing section 5 to the lower housing section 7. The annular cover 26 covers the further opening 19 of the lower housing section 7.

[0052] In the lower housing section 7, a displacement chamber 30 in the form of a cylinder 31 is arranged. This cylinder has a conical base 32 that forms its lower boundary. A further projection 33 extends downwards from the conical base 32. Another through-channel 34 extends from the lower end of this projection 33 into the cylinder 31. The cylinder 31 is precisely fitted into the lower housing section 7. The outer contour of the cylinder 31 corresponds to the inner contour of the lower housing section 7. The projection 33 is sealed on its outer circumference by an O-ring 35 on the inner circumference of the projection 21. At the top, the cylinder 31 is fixed in the lower housing section 7 by the connecting section 25.

[0053] A substantially disc-shaped piston 36 with a flat top and a bottom in the form of a shallow cone is arranged in the cylinder 31. A conical pin 37 projects downwards from the center of the bottom surface and can be inserted into the further projection 33 to create a seal. The piston 36 has a circumferential sealing lip 38. A rod-shaped piston actuator 39, also referred to as the piston rod 39, projects vertically upwards from the center of the top surface of the piston 36. The piston actuator 39 is arranged on the central axis of the hollow cylindrical housing lower part 3. It extends through the through-opening 14 into the spring chamber 6 and protrudes from the top of the opening 11.

[0054] The piston actuator 39 has four radially outwardly projecting, longitudinally extending guide ribs 41 on its outer circumference, of which two guide ribs 41.1 project further outward and two guide ribs 41.2 project less far outward. The two guide ribs 41.1 projecting further outward are guided in the axially extended guide grooves 15 of the through-opening 14. The two guide ribs 41.2 projecting less far outward are guided on the inner circumference of the through-opening 14 and each has a radially outwardly projecting step 41.3 at its base (see figure). Fig. 5a, c ).

[0055] Stage 41.3 is located in the uppermost position of piston 36, which is in Fig. 2 shown on the underside of cover 26.

[0056] A spring support 42 is attached to the upper end of the piston actuator 39. The piston actuator 39 and the spring support 42 are pre-assembled in Fig. 5a and b. The spring support 42 projects radially outwards from the piston actuator 39. It has a hollow cylindrical section 43 and four parallel legs 44 extending inwards from its inner circumference, which bear against the piston actuator 39. The piston actuator 39 has grooves 45 on its circumference, which have axial groove sections 45.1 extending downwards from its upper end and partially circumferential groove sections 45.2 extending from their lower ends. The legs 44 are inserted into the axial groove sections 45.1 with their inner ends (cf. Fig. 5c und d ) and the legs 44 are screwed into the partially circumferential groove sections 45.2 (cf. Fig. 5e The grooves 45 and the legs 44 form a bayonet connection 46, which holds the spring support 41 in a fixed position on the piston actuator 39.

[0057] The spring support 42 is also a guide element 47.

[0058] The outer circumference of the hollow cylindrical section 43 is as shown in Fig.3 The figure shows two wings 48 projecting outwards, formed by two arcuate sections 49. These are arranged on diametrically opposite sides of the hollow cylindrical section 43 and extend over the entire height or a portion thereof. Each arcuate section 49 has a circular arc-shaped curved section 50 in cross-section and outwardly inclined legs 51 extending from the ends of this section and connected to the hollow cylindrical section 43. The curved sections 50 form circular cylindrical second guide surfaces 52. Their outer radius of curvature corresponds to the radius of curvature of the first guide surface 17. The two curved sections 50 and the hollow cylindrical section 43 define two cavities 53 extending axially along the lower part of the hollow cylindrical housing 3.

[0059] The first guide surfaces 17 and the second guide surfaces 52 together form a first guide 54.

[0060] The guide grooves 15 form third guide surfaces 55 and the guide ribs 41 form fourth guide surfaces 56. The third guide surfaces 55 and the fourth guide surfaces 56 together form a second guide 57.

[0061] Between the two arc-shaped areas 49, the hollow cylindrical section 47 has two axially extending ribbing 58 on its outer circumference, which are diametrically opposite each other.

[0062] The spring support 42 is at the same time a spring seat 59 and a spring retainer 60 that fixes the spring seat 59 on the piston actuator 39.

[0063] The upper end of the piston actuator 39 is dome-shaped and forms a contact surface 61 for the lower end of a lifting rod of a drive device.

[0064] A coil spring 62 is arranged in the spring chamber 6 and is supported at the bottom by the limit 12 and at the top by the underside of the spring support 42. The coil spring 62 is installed under preload so that it pushes the piston actuator 39 upwards until the piston 36 with the steps 41.3 on its piston top 63 rests on the underside 64 of the cover 26 (see figure). Fig. 2 , 5c ).

[0065] The lower housing part 3 has an externally shaped, cup-shaped discharge sleeve 65. The upper housing section 5 and the lower housing section 7 are inserted into the discharge sleeve 65. The projection 21 extends downwards through a circular lower hole 66 from a conical housing base 67 of the discharge sleeve 65. The discharge sleeve 65 is closed at the top by a lid-like discharge transmitter 68, which has a circular upper hole 69 through which the circular cylindrical upper side wall 10 of the upper housing section 5 projects upwards. On its upper surface, the discharge transmitter 68 has an eye 70 for receiving the lower end of a discharge rod.

[0066] The upper housing part 4 contains according to Fig. 1 A lifting rod 71 rests against the upper surface of the contact surface 61. The lower end of the lifting rod 71 engages in the dome-shaped recess of the contact surface 61. A control knob 72 is fixed to the top of the lifting rod 71 and projects outwards from the upper end of the housing 2.

[0067] The lifting rod 71 passes through a central spindle bore 73 of a threaded spindle 74, which is located in the upper housing part 4. The threaded spindle 74 has an external thread 75 that can be screwed into an internal thread 76 of a lifting body 77, which is held at the bottom on a support 78 in the upper housing part 4. The lifting body 77 forms a spindle nut 79.

[0068] The lower end face of the threaded spindle 74 is an upper stop 80 for a stop element 81 in the form of an annular bead 82 on the outer circumference of the lifting rod 71.

[0069] The threaded spindle 74 is non-rotatably connected at its upper end to a driver 83, which engages in axial grooves 85 of a driver sleeve 86 by means of radially outwardly projecting ribs 84. The driver sleeve 86 is arranged concentrically to the threaded spindle 74 and rotatably mounted on the outer circumference of the lifting body 77. The driver sleeve 86 has a circumferential toothing 87 on its lower outer edge.

[0070] An adjusting sleeve 88 is pushed onto the drive sleeve 86. The adjusting sleeve 88 is rotationally fixed to the drive sleeve 86. The upper end of the adjusting sleeve 88 projects outwards from the upper end of the housing 2. There, the adjusting sleeve 88 has an adjusting ring 89 on its outer circumference, which has a further knurling 90 on its outer circumference.

[0071] A counter 91 in the form of a roller counter, which has a drive gear 92, is mounted on the first support 78. The number rollers of the counter 91 are visible from the outside of the housing 2 through a window in the upper part of the housing 4.

[0072] In the upper housing part 4, a cup-shaped holder 93 is arranged below the lifting body 77. The holder 93 includes a lower stop 94, which is supported by an overtravel spring 95 in the form of a coil spring, which is supported against a base of the holder 93. The lifting rod 71 is guided through central passages in the lower stop 94, through the overtravel spring 95, and through a central passage in the base of the holder 93.

[0073] When the adjusting sleeve 88 is turned, the drive sleeve 86 rotates along with it. The drive sleeve 86 screws the threaded spindle 74 into the housing-fixed internal thread 76, and the upper stop 80 moves up or down depending on the direction of rotation. This adjusts the distance between the upper stop 80 and the lower stop 94, which determines the dosing volume. The currently set dosing volume can be read on the counter 91, which is driven by the drive sleeve 86 via the drive gear 92.

[0074] At the upper edge of the housing top 4, next to the adjusting sleeve 88, a release button 96 is located on a release rod 97. The release rod 97 runs parallel to the lifting rod 71 through the housing top 4. Its lower end is pressed firmly into the eye 70 of the release transmitter 68 of the release sleeve 65, which is slidably mounted on the housing bottom 3.

[0075] In the upper housing part 4, a ejection spring 98, designed as a coil spring, is arranged, which is supported on one side by the housing 2 and on the other side by the ejection rod 97. The ejection spring 98 pushes the ejection rod 87 upwards, so that the ejection base 67 rests against the housing base 20.

[0076] The lower housing part 3 and the upper housing part 4 are connected to each other by a snap connection 99. This comprises according to Fig. 1 Preferably two spring-loaded hooks 100, which are bounded by slots in the circular cylindrical upper side wall 10 of the upper housing section 5 from the lower housing part 3. The hooks 100 are in Fig. 2 not shown, as these are opposite Fig. 1The vertical section is shown rotated 90° about the central axis of the lower housing part. Furthermore, the snap connection 99 comprises a circumferential inner step 101 on the inner circumference of an axially oriented receptacle 102 at the lower end of the upper housing part 4 for inserting the upper housing section 5 of the lower housing part 3. By snapping the spring-loaded hooks 100 behind the top surface of the inner step 101, the lower housing part 3 and the upper housing part 4 are connected to each other.

[0077] Before pipetting, the user can set the desired dispensing volume. To do this, he turns the setting ring 33 until the desired dispensing volume is displayed by the counter 91.

[0078] The user can attach a pipette tip 23 to the pipette 1 by pressing the pipette 1, with its seat 7, into an upper opening of the pipette tip 23. To pipette, the user first presses the operating button 72 downwards, so that the stop element 81 is moved from the upper stop 80 against the lower stop 94. This pushes the piston 36 downwards through the stroke rod 67 and pre-tensions the helical spring 62. The user then immerses the lower opening of the pipette tip 23 into the sample liquid and releases the operating button 72. As a result, the helical spring 62 pushes the piston 31 and the stroke rod 71 upwards until the stop element 81 rests against the upper stop 80. This draws a quantity of liquid corresponding to the set dosing volume into the pipette tip 23.

[0079] To dispense the desired amount of liquid, the user holds the pipette tip 23 with its lower opening over another container and presses the operating button 72 downwards again. After reaching the lower stop 94, the user can press the operating button 72 further, overcoming the resistance of the overtravel spring 95, to expel any remaining liquid from the pipette tip 23 by means of an overtravel.

[0080] The piston actuator 38 is guided downwards and upwards by the first guide 54 and the second guide 57 when the push rod 71 is moved downwards and upwards, thus preventing the piston 36 from tilting in the cylinder 31. Reference symbol list:

[0081] 1 Pipette 2 Housing 3 Hollow cylindrical housing lower part 4 Housing upper part 5 Upper housing section 6 Spring chamber 7 Lower housing section 8 Receiving chamber 9 Interior 10 Upper side wall 11 Circular opening 12 Limit 13 Step 14 Through-hole 15 Guide grooves 16 Base-like area 17 Guide surface 18 Lower side wall 19 Further opening 20 Conical housing bottom 21 Conical extension 22 Seat 23 Pipette tip 24 Through-channel 25 Connecting section 26 Circular disc-shaped cover 27 Enclosure 28 Internal thread 29 External thread 30 Displacement chamber 31 Cylinder 32 Conical bottom 33 Further extension 34 Further through-channel 35 O-ring 36 Circular disc-shaped piston 37 Conical pin 38 Sealing lip 39 Piston actuator 40 Piston rod 41, 41.1, 41.2 Guide ribs 41.3 Stage 42 Spring support 43 Hollow cylindrical section 44 Leg 45 Groove 45.1 Axial groove section 45.2 circumferential groove section 46 bayonet connection 47 guide element 48 wing 49 arcuate area 50 arcuate curved area 51 leg 52 second guide surface 53 cavity 54 first guide 55 third guide surface 56 fourth guide surface 57 second guide 58 knurling 59 spring seat 60 spring retainer 61 contact surface 62 coil spring 63 piston top 64 cover bottom 65 ejection sleeve 66 lower hole 67 conical ejector base 68 ejection transmitter 69 upper hole 70 eye 71 lifting rod 72 operating knob 73 spindle bore 74 threaded spindle 75 external thread 76 internal thread 77 lifting body 78 support 79 spindle nut 80 upper stop 81 stop element 82 annular bead 83 driver 84 projecting rib 85 axial groove 86 driver sleeve 87 toothing 88 adjusting sleeve 89 adjusting ring 90 further knurling 91 counter 92 drive gear 93 cup-shaped holder 94 lower stop 95 overtravel spring 96 ejector button 97 ejector rod 98 ejector spring 99 snap connection 100 hook 101 inner step 102 mount.

Claims

1. Single-channel lower part for a pipette comprising: • a hollow cylindrical housing lower part (3) with ∘ an interior space (9), ∘ an opening (11) at the upper end, ∘ a housing base (20) at the lower end, ∘ a projection (21) for attaching a pipette tip (23) which projects downwards from the housing base (20) and has a through-channel (24) extending from the lower end of the projection (21) into the interior space (9), and ∘ a spring chamber (6) which forms the interior space (9) or a part thereof, has the opening (11) at the top and at least one radially inwardly projecting boundary (12) with a through-opening (14) at the bottom, • a rod-shaped piston actuator (39) for displacing a piston (36) in a cylinder (31), wherein the piston actuator (39) is arranged at least partially in the spring chamber (6), in the axial direction of the extends to the hollow cylindrical housing lower part (3) and is aligned with the through-opening (14),• a contact surface (61) for a push rod (71) of a drive unit, which is arranged at the upper end of the piston actuator (39), • a spring support (41) which is connected to the piston actuator (39) above the limit (12) and projects radially outwards from it, • a coil spring (62) which is arranged in the spring chamber (6), supported at the top on the underside of the spring support (42) and at the bottom on the limit (12) and through which the piston actuator (39) extends, • a first guide (54) for guiding the piston actuator (39) in the axial direction of the hollow cylindrical housing lower part (3), which has at least a first guide surface (17) on the inner circumference of the spring chamber (6) and at least one second guide surface (52) on the outer circumference of a guide element (47) projecting radially outwards from and connected to the piston actuator (39).

2. Lower part according to claim 1, wherein the contact surface (61) has one or more of the following features: • the contact surface (61) is the top of the piston actuator (39) and / or the top of the spring support (42); • the contact surface (61) is the top of a piston head that is connected to the upper end of the piston actuator (39) and that has a larger cross-section than the adjacent area of ​​the piston actuator (39); • the contact surface (61) is dome-shaped.

3. Lower part according to claim 1 or 2, wherein the spring support (41) comprises a spring seat (59) held on the piston actuator (39) and a spring retainer (60) securing the spring seat (59) on the piston actuator.

4. Lower part according to one of claims 1 to 3, wherein the piston head and / or the spring support (41) is the guide element (47) and has the second guide surface (52) on the outer circumference.

5. Sub-part according to one of claims 1 to 4, wherein the first guide surface (17) and the second guide surface (52) are circular cylindrical.

6. Lower part according to one of claims 1 to 5, wherein (i) the spring chamber (6) has first guide surfaces (17) distributed symmetrically around its central axis, preferably two diametrically opposed, each only partially circumferential, on which the guide element bears with a single fully circumferential or with second guide surfaces (52) distributed symmetrically around the piston actuator (39), preferably two diametrically opposed, each only partially circumferential, or (ii) the spring chamber (6) has only a single fully circumferential first guide surface (17) on which the guide element (47) bears with second guide surfaces (52) distributed symmetrically around the piston actuator (39), preferably two diametrically opposed, each only partially circumferential, on which it bears.

7. Lower part according to one of claims 1 to 6, wherein the guide element (47) has a hollow cylindrical section (42) and at least one second guide surface (52) on the outer circumference of the hollow cylindrical section (42) and the hollow cylindrical section accommodates the piston actuator (39).

8. Lower part according to claim 7, wherein the second guide surfaces (52) are provided on the outside of wings (48) which project outwards from the circumference of the hollow cylindrical section (43).

9. Lower part according to claim 8, wherein the wings (48) have cavities (53) extending parallel to the piston actuator (39) with a circular arc cross-section.

10. Lower part according to one of claims 1 to 9, wherein the guide element (47) has a snap connection and / or a positive locking connection with the piston actuator (39).

11. Lower part according to one of claims 1 to 10, wherein the limit (12) is a shoulder (13) circumferentially or partially around the inner circumference of the lower part of the housing (3).

12. Lower part according to one of claims 1 to 11, wherein the lower housing part (3) has a hollow cylindrical upper housing section (5) comprising the spring chamber (6) which forms part of the interior (9), and the lower housing part has a hollow cylindrical lower housing section (7) comprising a receiving chamber (8) which is bounded at the bottom by the housing base (20) and forms a further part of the interior (9), a cylinder (31) is arranged in the receiving chamber (8), the cylinder is connected at the bottom to the through-channel (24) of the projection (21), a piston (36) is arranged in the cylinder, the piston bears against the inner surface of the cylinder (31) in a sealing manner at its circumference and is displaceable in the axial direction of the cylinder, and a piston actuator (39) in the form of a piston rod (40) is connected to the piston (36) which extends upwards from the piston through the through-opening (14) into the upper housing section (5). extends into.

13. Lower part according to claim 12, wherein the receiving space (8) of the lower housing section (7) has a larger diameter than the spring space (6) of the upper housing section (5).

14. Lower part according to claim 12 or 13, wherein a connecting section (25) connects the lower edge of the upper housing section (5) to the upper edge of the lower housing section (7), the connecting section (25) comprising an annular disk-shaped cover (26) and a hollow cylindrical surround (27) projecting downwards from the outer edge of the cover, the upper housing section (5) being connected to the top of the cover (26), the surround (27) being connected to the upper edge of the lower housing section (7), and the cover (26) covering the receiving space (8) at the top.

15. Lower part according to one of claims 1 to 14, wherein the piston actuator (39) has at its lower end a device for connecting to the upper end of a tip piston which is inserted into a pipette tip (23) which can be clamped onto the extension (21).

16. Lower part according to one of claims 1 to 15, wherein a second guide (57) of the piston actuator (39) is provided in the axial direction of the hollow cylindrical housing lower part (3), which has at least a third guide surface (55) at the through-opening (14) and at least a fourth guide surface (56) on the circumference of the piston actuator (39).

17. Lower part according to one of claims 1 to 16, wherein the through-opening (16) has one or more of the following features: • the through-opening (14) has a circular cross-section; • the through-opening (14) has two diametrically opposed guide grooves (15) and the piston actuator (39) has at least two diametrically opposed, outwardly projecting guide ribs (41) on its outer circumference which engage in the guide grooves.

18. Pipette comprising an upper part and a single-channel lower part according to any one of claims 1 to 17, wherein the upper part comprises a housing upper part (4), an operating button (72) on the outside of the housing upper part (4), a drive unit arranged in the housing upper part (4) and operatively connected to the operating button (82), and a movable stroke rod (71) of the drive unit, the lower end of which is accessible from the outside at a further opening of the housing upper part (4), wherein the upper part and the single-channel lower part are configured to be brought into a connected position in which the lower end of the stroke rod (71) contacts the contact surface (61) of the piston actuator (39), and a connecting device is provided which connects the upper part and the lower part together in the connected position.

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