Pipette with adjustable pipetting volume and locking system

Abstract

The invention relates to a pipette (10) with a housing (20) for receiving a displacement device, wherein the displacement device comprises a displacement chamber (24) and a movable limit (26) for limiting a pipetting stroke of the pipette (10). The pipette (10) further comprises an operating element (12) for setting a pipetting volume of the pipette (10) by moving the limit (26) in the housing (20) and for performing a pipetting operation, wherein the operating element (12) is operatively connected to a piston movable in the displacement chamber (24) of the displacement device, a counter (30) for displaying the set pipetting volume, and a locking mechanism (40) for locking and / or unlocking a volume setting by the operating element (12).The locking mechanism (40) comprises a locking slide (42) which is operatively connected to a locking ring (44) coupled to the counter (30) in such a way that the locking slide (42) allows an adjustment of the pipetting volume in a first position and in a second position prevents rotation of the locking ring (44) and the counter coupled to the locking ring (44).

Description

[0001] The invention relates to a pipette with an adjustable pipetting volume and a locking system for locking the set pipetting volume according to the preamble of the independent claim.

[0002] Pipettes are used, particularly in laboratories, for the controlled aspiration and dispensing of liquids. For this purpose, a pipette tip with an upper opening is clamped onto a seat of the pipette. The seat is preferably shaped as a conical or cylindrical projection on the pipette body. The pipette tip can aspirate and dispense liquid through a lower opening. Air-cushion pipettes comprise an air displacement device that communicates with the pipette tip through a hole in the seat. The displacement device moves an air cushion, causing liquid to be drawn into and expelled from the pipette tip. For this purpose, the displacement device has a displacement chamber with a movable boundary. The displacement device is usually a cylinder with a piston that can be moved within it.

[0003] After use, the pipette tips are detached from the holder and replaced with a fresh one. This prevents contamination during subsequent doses. Most pipette tips have an ejection mechanism that allows for easy disposal by pressing a button without touching the tip. Disposable pipette tips are readily available in inexpensive plastic versions.

[0004] The movable stop is coupled to a drive mechanism that moves the piston within the cylinder. The drive mechanism includes a push rod that can be moved between upper and lower stops by means of a stop element. At the start of air intake into the displacement chamber, the stop element is at the lower stop. At the start of air displacement from the cylinder, the stop element rests against the upper stop. The amount of liquid drawn in or discharged depends on the stroke of the movable stop and thus on the stroke of the push rod.

[0005] In principle, systems for blocking the adjustment of a set pipetting volume, also known as volume locks, are known in the art. Volume lock systems already exist that prevent the counter and / or the volume adjustment from locking by means of a positive connection between a detent element and the adjustment mechanism. Furthermore, volume lock systems are known in the art that achieve a volume lock using a friction clutch. However, a disadvantage of these systems is that a relatively high force is required to lock the volume, and that a friction clutch can be overcome too easily, thus not providing reliable locking of the set pipetting volume.

[0006] Furthermore, volume-lock systems are known that require the control element to be pressed throughout the entire volume setting process in order to unlock the volume setting. While this variant offers a high degree of security against unintentional changes to the set pipetting volume, it requires two-handed operation of the pipette to simultaneously hold down the unlocking element and adjust the volume.

[0007] Other volume-lock systems can be unlocked by pulling the control knob upwards into a detent. During pipetting, this detent releases, and the volume setting is locked again. This system also requires two-handed operation: one hand to hold the pipette and the other to pull the control knob upwards. Furthermore, some pipettes have a system where the volume lock can be unintentionally activated when the control knob is turned to adjust the pipetting volume. Additionally, user feedback indicates that the fact that the control knob also unlocks the volume setting is not intuitive.

[0008] From EP 2 659 978 A1, an air cushion pipette with an adjustable pipetting volume and a locking element for locking the set pipetting volume is known. The pipette has a rod-shaped housing, a seat for releasably holding a pipette tip at the lower end of the housing, and a displacement device with a displacement chamber and a movable stop therein. The pipette further has a drive mechanism for moving the movable stop of the displacement device and a locking element with which the drive mechanism can be locked against unwanted adjustment of the set pipetting volume.

[0009] EP 3 749 456 B1 discloses a device for locking a volume adjustment screw for a pipetting system. The device for locking a volume adjustment screw for a pipetting system comprises, on the one hand, a claw coupling system for holding the position of the volume adjustment screw, wherein the pipetting system has the following: - a first gear, which includes the first teeth, - a second gear comprising two teeth, wherein the first gear is a ratchet gear designed to be rotationally fixed with respect to a fixed part of the pipetting system, and the second gear is designed to be rotationally fixed to the adjusting screw, or vice versa, - elastic return means capable of returning the first and second gears to each other so that the first teeth engage with the second teeth, and a system for controlling the claw coupling holding system, wherein the control system comprises the following: - a position selector designed to be rotated between three positions along a longitudinal central axis of the pipetting system, namely a free adjustment position, a fine adjustment position and a locking position, - a control element rigidly connected to the position selector, wherein the control element interacts with the ratchet wheel of the claw coupling system, so that: a) when the selector is in the free adjustment position, the control element keeps the ratchet wheel axially spaced from the other wheel of the jaw coupling system by counteracting the force generated by the elastic return means, so that the first and second teeth do not engage with each other, b) when the selector is in the fine-adjustment position, the control element allows the ratchet wheel to move away and then, during a transition from one tooth to another caused by the rotation of this other wheel, to move axially closer to the other wheel, and c) when the selector is in the locking position, the control element axially locks the ratchet wheel to prevent the first and second teeth from disengaging.

[0010] From DE 10 2022 104 546 A1, a pipette with a housing for receiving a displacement device is known, wherein the displacement device comprises a displacement chamber and a movable limit for limiting a pipetting stroke of the pipette. The pipette further has an operating element for setting a pipetting volume of the pipette by moving the limit in the housing and for executing a pipetting operation, wherein the operating element is operatively connected to a piston that can be moved in the displacement chamber of the displacement device. The pipette further includes a counter for displaying the set pipetting volume and a locking mechanism for locking and / or unlocking a volume setting by the operating element.The control element is designed to move the locking mechanism into a locked position and prevent any adjustment of the pipetting volume when the control element is actuated during a pipetting process.

[0011] DE 10 2022 116 308 A1 describes a pipetting device for aspirating and dispensing fluid volumes, comprising a displacement device with a displacement element and a displacement housing. The pipetting device has an adjustment device for changing the stroke of the displacement element. The stroke of the displacement element can be adjusted, and the corresponding adjustment value is displayed by means of an adjustment indicator. By means of a coupling device, the adjustment device is coupled to a volume indicator and decoupled from the adjustment indicator in an operating state, whereas in an adjustment state, the adjustment device is coupled to the adjustment indicator and decoupled from the volume indicator.

[0012] The invention is based on the objective of overcoming the disadvantages known from the prior art and proposing an operating concept for a pipette which enables a simple, intuitive locking of the volume adjustment with low operating forces and at the same time reliably protects the user of the pipette from an unwanted adjustment of the set pipetting volume.

[0013] The problem is solved by a pipette with a housing for a displacement device, the displacement device comprising a displacement chamber and a movable stop for setting the pipetting stroke. The pipette also features a control element for setting the pipetting volume by moving the stop within the housing and for executing a pipetting operation. This control element is operatively connected to a piston that can be moved within the displacement chamber of the displacement device. Furthermore, the pipette includes a counter for displaying the set pipetting volume and a locking element for locking and / or unlocking the volume setting via the control element.

[0014] According to the invention, the locking mechanism comprises a locking slide which is operatively connected to a locking ring that can be coupled to the counter, such that the locking ring allows adjustment of the pipetting volume in a first position and, in a second position, prevents rotation of the locking ring and the counter that can be coupled to the locking ring. By locking the counter by fixing the locking ring, which is at least indirectly coupled to the counter, the volume adjustment can be effectively blocked, thus protecting the pipette against unintentional adjustment of the pipetting volume. An operator can easily move the pipette from the locked operating state to the unlocked operating state, thereby preventing accidental adjustment of the pipetting volume.

[0015] According to the invention, the locking mechanism comprises a blocking element which, in the locked position of the locking mechanism, prevents rotation of the counter wheels. The locking element allows the locking ring to be easily fixed in its position, thereby preventing rotation of the counter wheels and thus any adjustment of the pipetting volume. In particular, a positive-locking connection is established between the blocking element and the locking ring to prevent rotation of the counter wheels. According to the invention, the locking ring is provided with a first stop contour and a second stop contour, wherein the locking slide rests against the first stop contour in the locked position of the locking mechanism and against the second stop contour of the locking ring in the unlocked position. This provides both visual and haptic feedback to the operator indicating that the locking slide is in the unlocked or locked position. This results in particularly user-friendly locking and unlocking of the pipette's volume adjustment.

[0016] The additional features listed in the dependent claims enable advantageous embodiments and improvements of the pipette specified in the independent claim.

[0017] Preferably, the locking element comprises a bearing element and at least one arm extending from the bearing element, preferably two arms extending from the bearing element, wherein the locking element is rotatably mounted on the bearing element. This allows the locking element to be easily engaged with the locking ring, with the arm either engaging directly with the locking ring and locking it, or being held in place by another element, whereby the interaction of the other element and the arm locks the locking ring and thus prevents volume adjustment.

[0018] It is particularly preferred if the arm of the locking element has a locking cam that engages in a cam contour on one of the counter wheels. Such a locking cam allows for a simple, positive-locking connection between the arm of the locking element and the locking ring. This locks the counter and reliably prevents unintentional adjustment of the pipetting volume.

[0019] In an advantageous further development of the pipette, a catch contour is formed on the first stop contour of the locking ring. This catch contour secures the locking cam and prevents it from lifting off the cam contour on one of the counter wheels. This prevents the locking cams on the arm of the locking element from lifting off the cam contour on the counter wheels. Thus, even under considerable force, further rotation of the counter wheels is reliably prevented, thereby eliminating any unintentional changes to the pipetting volume.

[0020] It is particularly preferred if a recess is formed on the locking contour in which the locking cam is at least partially received in the locked position of the locking slide of the locking mechanism. This creates a positive fit that receives the locking cam with virtually no play and thus ensures secure engagement of the locking cam with the cam contour on the counter wheels of the counter. This prevents unintentional release of the locking mechanism.

[0021] According to an advantageous embodiment of the pipette, the locking contour prevents radial outward movement of the locking cam by pressing an engagement contour formed on a radially inward-oriented surface of the locking cam into the cam contour on one of the counter wheels. This creates a positive locking connection between the engagement contour on the locking cam and the cam contour on the counter wheels, which prevents adjustment of the counter and the pipetting volume. By locking the arm of the blocking element through the engagement of the locking cam, lifting of the blocking element arm and the associated unlocking are prevented.

[0022] In an advantageous embodiment of the pipette, the locking element is biased by a pressure element, in particular by a spring, such that the arm of the locking element is pressed against one of the counter wheels. The arm of the locking element, with its detent cam, is thereby pressed by the pressure element against the cam contour of the counter. This allows for easy adjustment of the pipetting volume when the locking mechanism is unlocked, provided the pressure force is overcome. Furthermore, this ensures that the arm and the detent cam formed on the arm of the locking element can be easily fixed to the cam contour of the counter wheels when locking is desired, thus preventing any volume adjustment.

[0023] In an advantageous embodiment of the invention, it is provided that, in an unlocked position of the locking slide, movement of the detent cam is permitted radially outward, thereby enabling adjustment of the pipetting volume and a corresponding rotation of the counter wheels. Since the detent cam is freely movable radially outward in the unlocked locking state of the locking slide, the detent cam can lift off the cam contour and the counter wheels can be rotated until the detent cam engages in the next recess of the counter wheel's cam contour, thus enabling a volume adjustment by one counting unit. With further rotation, the detent cam can engage the counter wheel in specific increments of one counting unit, allowing the detent cam to be locked in the counter mechanism.

[0024] According to an advantageous embodiment of the pipette, the counter wheels are engaged with a transmission gear of a volume adjustment mechanism. Since the pipetting volume is typically set via the operating knob or an adjustment wheel surrounding the operating knob, which is at least indirectly coupled to the counter, the transmission gear ensures that locking the counter also locks the pipetting volume adjustment. This allows for simple locking and unlocking of the volume adjustment by means of a locking ring coupled to the counter.

[0025] In an advantageous embodiment of the pipette, a radially inwardly extending contour of the locking slide engages positively in a recess between a first stop contour and a second stop contour on the locking ring. This allows for a positive-locking connection between the locking slide and the locking ring of the locking mechanism to be established in a structurally simple manner.

[0026] According to an advantageous embodiment of the pipette, the locking slide of the locking mechanism is aligned perpendicular to a longitudinal axis of the pipette. This allows for particularly user-friendly positioning of the locking slide, making it easier for the operator to lock or unlock the volume adjustment of the pipette.

[0027] For ease of use, the pipette is advantageously equipped with a finger hook on the housing, with the locking slide of the locking mechanism located on the opposite side of the housing. This allows for particularly simple and convenient operation, especially one-handed operation of the pipette. Specifically, the pipette can be held by the finger hook while the locking mechanism is moved from the locked to the unlocked position using the fingers of the same hand, and the pipetting volume is then set by turning the control knob.

[0028] In an advantageous embodiment of the invention, the locking ring is arranged coaxially to the counter wheels on a counter axis. This allows for simple rotation of the locking ring relative to the counter wheels, enabling the locking mechanism to be switched from the unlocked operating state to the locked operating state by rotating the locking ring.

[0029] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise specified in individual cases.

[0030] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Identical components or components with the same function are identified by the same reference numerals in the different figures. The figures show: Fig. 1 a sectional view of a pipette according to the invention with an adjustable pipetting volume and locking system for temporary and reversibly releasable locking of a volume setting of the pipette; Fig. 2 a preferred embodiment of a counter of such a pipette with a locking mechanism for locking the volume adjustment of the pipette in a first switching position; Fig. 3 another preferred embodiment of a counter of such a pipette with a locking mechanism for locking the volume adjustment of the pipette in a second switching position; Fig. 4 a section through a locking plane of the pipette in a locked switching position of the locking mechanism in which a volume adjustment is locked; and Fig. 5 a section through a locking plane of the pipette in an unlocked switching position of the locking mechanism in which volume adjustment is possible.

[0031] Fig. Figure 1 shows a sectional view of a pipette 10 according to the invention. The pipette 10 has a pipette top 21 and a coupling to the pipette top 21, in Fig. 1. The lower part 21 (not shown) comprises a housing 20, wherein an operating element 12, preferably an operating knob 14, protrudes through an opening in the housing 20 on an end face of the housing opposite the lower part of the pipette. The operating element 12 has two functions: First, the operating element 12 serves to set a pipetting volume, i.e., the amount of liquid that is to be aspirated by the pipette 10 and subsequently dispensed during a pipetting process. The pipetting volume is set by rotating the operating element 12, whereby the set pipetting volume is increased by rotating the operating element 12 in a first direction of rotation and decreased by rotating it in the opposite direction. Due to the design, the adjustable pipetting volume lies between a minimum and a maximum pipetting volume.Secondly, the control element 12 serves for the aspiration and subsequent dispensing of liquid during a pipetting process, wherein an operating knob 14 of the control element 12 is moved axially along a central axis of the pipette. Furthermore, a finger hook 16 is provided on the housing 20 to facilitate holding the pipette 10. Additionally, an ejector 18 is arranged on the housing 20, preferably on a side opposite the finger hook 16, to eject a used pipette tip from a receptacle on the lower part of the pipette after a pipetting process. For this purpose, the ejector 18 is operatively connected to an ejection linkage 19, which presses against an end face of the pipette tip and thus initiates the ejection of the pipette tip.Several functions, in particular volume adjustment, aspiration and dispensing of the liquid volume, and / or ejection of the pipette tip, can be combined in a single control knob 14, allowing for simple and convenient operation with just one knob. Alternatively, the function can be distributed across several components of the control element 12, and in particular, an additional ejector 18 for ejecting a used pipette tip can be provided alongside the control knob 14. Furthermore, the control element 12 may include a control knob 14 for aspiration and dispensing of the liquid and a movable element for adjusting the pipetting volume, in particular a rotary knob for adjusting the pipetting volume.

[0032] The housing 20 has a displacement device, the displacement device comprising a displacement chamber 24 and a movable limit 26 for limiting the pipetting stroke. The control element 12 is configured to set a pipetting volume of the pipette 10 by moving the limit 26 within the housing 20 and to execute a pipetting operation. The control element 12 is connected via a stroke rod 22 to a movable element within the displacement chamber 24 of the displacement device. Fig. 1 piston (not shown), in operative connection. The pipette 10 further comprises a counter 30 for displaying the set pipetting volume and a locking mechanism 40 for locking and / or unlocking a volume setting by means of the control element 12.

[0033] In this embodiment, the counter 30 comprises a first counter wheel 32, a second counter wheel 34, a third counter wheel 36 and a fourth counter wheel 38. However, embodiments with fewer or more than four counter wheels are also possible.

[0034] The locking mechanism 40 comprises a locking slide 42 for locking or unlocking the locking mechanism 40. The locking mechanism 40 further comprises a locking ring 44, into which the locking slide 42 engages in order to transfer the volume adjustment 60 of the pipette 10 from a locked operating state to an unlocked state or from an unlocked state to a locked operating state.

[0035] A transparent display window is integrated into the housing 20 to allow a view of the counter 30 from the outside and to read the set pipetting volume. A movable stop 26 for the stroke rod 22 is provided in the housing 20, with a shoulder on the stroke rod 22 bearing against the movable stop 26 and thus limiting the stroke of the piston. The pipetting volume is set by moving the stop 26.

[0036] The pipette lower part comprises a displacement chamber 24 into which the piston, which can be actuated via the control element 12 and is connected to the stroke rod 22, is immersed. The pipette lower part also has a clamping area for receiving a pipette tip, the pipette tip being released from the clamping area and thus ejected by actuating the control element 12 via the ejection rod 19.

[0037] To change the pipetting volume of the pipette 10, the locking slide 42 of the locking mechanism 40 is first moved to an unlocked position. An unlocked position is defined as a position of the locking mechanism in which the control element 12 can be rotated, thus changing the pipetting volume. After setting the desired pipetting volume, the control element 12 is actuated to perform a pipetting operation. Actuating the control element 12 in this context means pressing the control element 12 and thereby axially displacing it along a longitudinal axis 72 of the pipette 10. This longitudinal axis runs vertically in the plane of the drawing, from the control element 12 through the pipette upper part 21 and the pipette lower part to a receiving opening at the end of the pipette lower part opposite the pipette upper part 21.

[0038] In Fig. Figure 2 shows a locking mechanism 40 of the pipette 10 for locking a set pipetting volume in a three-dimensional representation. The locking mechanism 40 comprises a locking slide 42 and a locking ring 44 operatively connected to the locking slide 42. The locking ring 44 locks the volume adjustment 60 of the pipette 10 by the operating element 12, in particular by turning the operating knob 14, by moving the locking slide 42 from an unlocked position to a locked position. The locking ring 44 and the counter wheels 32, 34, 36, 38 of the counter 30 are arranged on a common counter axis 31. The locking ring 44 is in operative connection with a blocking element 50, which can engage in the counting wheels 32, 34, 36, 38 of the counter 30 and thus lock the volume adjustment 60 of the pipette 10.The locking element 50 has a bearing element 51, by which the locking element 50 is rotatably mounted on a pivot point 52 in an interior space of the housing 20 of the pipette 10. The locking element 50 has a first arm 53, which serves to lock the volume adjustment 60. The locking element 50 may also have a second arm 54 opposite the first arm 53, which can be used to actuate or press the locking element 50 against the counter wheels 32, 34, 36, 38. The pipette 10 may also have a switch 28, with which different adjustment speeds can be set for the volume adjustment 60. In the [reference to be added] Fig. In the embodiment shown in Figure 2, the locking mechanism 40 is shown in an unlocked switching position, in which the locking slide 42 rests against a second stop contour 48 of the locking ring 44 and the pipetting volume can be adjusted via the volume adjustment 60.

[0039] Fig. Figure 3 shows a further preferred embodiment of a locking mechanism 40 for a pipette according to the invention. With essentially the same structure as described above, this embodiment is further modified by the following methods: Fig. In this embodiment, an additional switch 28, which allows for setting different adjustment speeds during volume adjustment 60, is omitted. Therefore, any adjustment of the speeds during volume adjustment is independent of the proposed locking mechanism 40. Furthermore, the locking mechanism 40 is in Fig. 3 shown in a locked switching position, in which the locking slide 42 rests against a first stop contour 46 of the locking ring 44 and the volume adjustment 60 is locked.

[0040] Fig. Figure 4 shows a section through a locking plane of the pipette 10 in a locked switching position of the locking mechanism 40, in which a volume adjustment 60 is prevented. In this position, a radially inwardly extending contour 74 on the locking slide 42 engages in a recess 70 between the first stop contour 46 and the second stop contour 48 on the locking ring 44. In the locked switching position, the contour 74 is pressed against the first stop contour 46 of the locking ring 44.In this process, a locking cam 59 formed on the first arm 53 of the locking element 50 is positively engaged in a recess 56 by a catch contour 58 formed on the first stop contour 46 and presses an engagement contour 57 formed on a radially inner side of the locking cam 59 into a cam contour 39 on one of the counting wheels 32, 34, 36, 38 of the counter 30, thereby establishing a positive connection between the locking cam 59 of the locking element and the cam contour 39 of the counter 30 and locking the counting wheels 32, 34, 36, 38 against rotation. By locking the counter wheels 32, 34, 36, 38 of the counter 30 and a transmission gear 64 which engages both with a gear of the volume adjustment 60 and with the counter 30, the entire transmission train of the volume adjustment 60 is locked.Thus, rotation of the control knob 14 connected to the volume adjustment 60 is no longer possible, and the pipette 10 is protected against unwanted changes to the set pipetting volume. The locking contour 58 on the first stop contour of the locking ring 44 prevents, in particular, the first arm 53 of the locking element 50 and the detent cam 59 formed thereon from deflecting radially outwards and thus disengaging the positive locking between the detent cam 59 and the cam contour 39 of the counter 30. The locking element 50 is preferably pre-loaded by a pressure element 68 such that the detent cam 59 on the first arm 53 of the locking element 50 is pressed against the counting wheels 32, 34, 36, 38 of the counter 30. The pressure element 68 can, in particular, be designed as a torsion spring.

[0041] In Fig. 5 is the locking mechanism from Fig.Figure 4 shows the pipetting volume in an unlocked switching position, in which the pipetting volume can be adjusted by means of the control knob 14 and the volume adjustment elements 60 to move the movable limit of the stroke rod 22. In this position, the radially inwardly extending contour 74 engages a recess 70 on the locking slide 42 between the first stop contour 46 and the second stop contour 48 on the locking ring 44. In the unlocked switching position, the contour 74 is pressed against the second stop contour 48 of the locking ring 44, and the locking ring 44 is rotated such that the recess 56 on the catch contour 58 of the locking ring 44 is no longer engaged with the detent cam 59.Although the locking cam 59 continues to be pressed against the cam contour 39 of the counter 30 by the pressure element 68, the radial outward movement of the locking cam 59 is no longer blocked. Therefore, when the pipetting volume is adjusted, the locking cam 59 lifts out of the cam contour 39 and, as the volume adjustment 60 is turned further, engages in the next recess of the cam contour 39, thus changing the pipetting volume by one unit. This process is repeated until the desired pipetting volume is set. If the operator wishes to secure the newly set pipetting volume and to secure the pipette 10 against an unintentional adjustment of the pipetting volume, the locking slide 42 is pushed back into the locked position after the volume adjustment, whereby the locking cam 59 is again secured by the catch contour 58 and prevents rotation of the counter wheels 32, 34, 36, 38 of the counter 30. Reference symbol list 10 pipettes 12 Control element 14 Control knob 16 finger hooks 18 drop bombs 19 drop rods 20 cases 21 Top 22 Lifting rod 24 Displacement chamber 26 movable limits 28 switches 30 counter 31 Counter shaft 32 first counting wheel 34 second counter wheel 36 third counting wheel 38 fourth counting wheel 39 Cam contour 40 Locking mechanism 42 locking gates 44 Locking ring 46 first stop contour 48 second stop contour 50 blocking element 51 Bearing element 52 Pivot point 53 first arm 54 second arm 56 Exclusion 57 Intervention contour 58 Catch contour 59 locking cams 60 volume adjustment 62 wave 64 Transmission gear 66 Return element 68 Pressure element 70 Exclusion 72 Longitudinal axis 74 contour

Claims

[1] Pipette (10), comprising - a housing (20) for accommodating a displacement device, wherein the displacement device comprises a displacement chamber (24) and a displaceable limiter (26) for limiting a pipetting stroke of the pipette (10), - an operating element (12) for adjusting a pipetting volume of the pipette (10) by displacing the limit stop (26) in the housing (20) and for carrying out a pipetting process, wherein the operating element (12) is operatively connected to a piston displaceable in the displacement chamber (24) of the displacement device, - a counter (30) to display the set pipetting volume, - a locking mechanism (40) for locking and / or unlocking a volume setting by the control element (12), - wherein the locking mechanism (40) comprises a locking slide (42) which is operatively connected to a locking ring (44) which can be coupled to the counter (30) in such a way that the locking ring (44) enables an adjustment of the pipetting volume in a first position and, in a second position, a rotation of the locking ring (44) and locks the counter (30) which can be coupled to the locking ring (44), wherein the locking mechanism (40) comprises a blocking element (50) which, in the locked position of the locking mechanism (40), prevents a rotation of the counting wheels (32, 34, 36, 38) of the counter (30), characterized by , that - a first stop contour (46) and a second stop contour (48) are formed on the locking ring (44), wherein the locking slide (42) rests on the first stop contour (46) in the locked position of the locking mechanism (40) and on the second stop contour (48) of the locking ring (44) in the unlocked position. [2] Pipette (10) according to claim 1, characterized by that the blocking element (50) has a bearing element (51) and at least one arm (53, 54) extending from the bearing element (51), wherein the blocking element (50) is rotatably mounted on the bearing element (51). [3] Pipette (10) according to claim 2, characterized by that a locking cam (59) is formed on the arm (53) of the blocking element (50), which engages in a cam contour (39) on one of the counting wheels (32, 34, 36, 38). [4] Pipette (10) according to claim 3, characterized by that a catch contour (58) is formed on the first stop contour (46) of the locking ring (44), which catch contour fixes the locking cam (59) and prevents the locking cam (59) from being lifted off the cam contour (39) on one of the counting wheels (32, 34, 36, 38). [5] Pipette (10) according to claim 4, characterized bythat a recess (56) is formed on the catch contour (58), in which the locking cam (59) is at least partially received in the locked position of the locking mechanism (40). [6] Pipette (10) according to claim 4 or 5, characterized by that the catching contour (58) prevents a movement of the locking cam (59) radially outwards, such that an engagement contour (57) formed on a radially inwardly oriented surface of the locking cam (59) is pressed into the cam contour (39) on one of the counting wheels (32, 34, 36, 38). [7] Pipette (10) according to one of claims 2 to 6, characterized by that the blocking element (50) is loaded by a pressing element (68) such that the first arm (53) of the blocking element (50) is pressed against one of the counting wheels (32, 34, 36, 38) of the counter (30). [8] Pipette (10) according to one of claims 3 to 7, characterized bythat in the unlocked position of the locking slide (42) of the locking mechanism (40), a movement of the locking cam (59) radially outwards is made possible, whereby a rotation of the counting wheels (32, 34, 36, 38) of the counter (30) and an associated adjustment of the pipetting volume is made possible. [9] Pipette (10) according to one of claims 1 to 8, characterized by that the counting wheels (32, 34, 36, 38) of the counter (30) are in engagement with a transmission gear (64) of a volume adjustment (60). [10] Pipette (10) according to one of claims 1 to 9, characterized by that a radially inwardly extending contour (74) of the locking slide (42) engages positively in a recess (70) between a first stop contour (46) and a second stop contour (48) on the locking ring (44). [11] Pipette (10) according to one of claims 1 to 10, characterized bythat the locking slide (42) of the locking mechanism (40) is aligned perpendicular to a longitudinal axis (72) of the pipette (10). [12] Pipette (10) according to one of claims 1 to 11, characterized by that a finger hook (16) is formed on the housing (20), wherein the locking slide (42) of the locking mechanism (40) is arranged on a side of the housing (20) opposite the finger hook (16). [13] Pipette (10) according to one of claims 1 to 12, wherein the locking ring (44) is arranged coaxially to the counting wheels (32, 34, 36, 38) of the counter (30) on a counter axis (31).

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