EP2978533B1 - Ejection mechanism for a positive displacement pipette - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of positive displacement pipetting.

Such systems are intended to cooperate with consumables of the capillary-piston type, whose piston is intended to be directly in contact with the sample to be taken, before being ejected or reused. Positive displacement systems therefore have a different design from that of more conventional air displacement systems in which the piston is an integral part of the system.

The invention relates more specifically to the ejection function of the capillary-piston assembly. It applies to all the different types of sampling system, namely in particular pipettes, manual or motorized, as well as PLCs.

STATE OF THE PRIOR ART

Positive displacement pipettes are usually used for sampling viscous, volatile liquids and / or contaminants. Their combination with "capillary-piston" type consumables makes it possible to avoid contamination of the pipette. It is the same for automata operating on the same principle.

Such a positive displacement pipette is known from the French patent application FR 2,446,672 .

On positive displacement pipettes known from the prior art, there is provided a control rod whose low end controls the displacement of a device for gripping the upper end of a piston belonging to a capillary assembly. piston for cooperating with the pipette. This gripping device is also called "gripper".

The pipette is designed to be able to exercise two successive downward strokes with the control rod, via a control button arranged at its high end. The first stroke of the control rod corresponds to the dispensing stroke of the sampled sample. It is performed by opposing the restoring force of a first spring, preferably compression. The second stroke of the control rod corresponds to the presentation and opening of the piston gripper. It is performed by opposing the restoring force of a second spring, preferably compression, arranged in the same direction as the first spring and having a significantly higher stiffness.

More precisely, this second race has the effect of extracting the jaws / jaws of the clamp from a sheath that encloses them. Once the jaws released from their sheath, they can easily let the upper end of the piston during the installation of the consumable on the pipette, which also simultaneously sees the fitting of the capillary on the tip of the pipette.

The first phase of raising of the control rod, under the effect of the restoring force of the second spring, has the effect of retracting the jaws into the sheath of the clamp, with the upper end of the piston held by the jaws. tight position. The second phase of raising of the control rod, under the effect of the restoring force of the first spring of lower stiffness, leads to the displacement of this rod as well as the clamp enclosing the piston to a high position, relative to to the pipette body.

To perform a sample collection, the operator must again perform the first stroke of the control rod with the onboard piston, until the total compression of the first spring bringing the piston to its low sampling point. A continuation of the race at this stage, that is to say an accidental start of the second race against the second spring, would result in an excessive displacement of the piston downwards, and lead to an error in the amount of sample taken. Excessive over-stroke of the piston could even lead to the accidental ejection of the piston and the capillary, due to the release of the jaws of the clamp by the sleeve which surrounds them, and the support of these jaws on the capillary. Such an ejection is no only problematic in terms of productivity, but also generates non-negligible risks of liquid projection when the capillary-piston assembly falls into a liquid container.

When the piston has reached its low point at the end of the first stroke, the consumable is plunged into the liquid to be withdrawn. To ensure the sampling, the operator then gradually releases the pressure exerted by his thumb on the control button, which allows the control rod and the piston to go up under the effect of the restoring force of the first spring. During this ascent, the liquid in contact with the lower end of the piston is introduced into the capillary.

For dispensing, the operator carries out the first stroke of the control rod by pressing his thumb on the control button, placing the capillary in the receptacle for receiving the liquid. Here again, in case of over-stroke of the piston, it may be accidentally ejected with the capillary, thus generating again a risk of accidental projection of liquid.

Finally, once the liquid dispensing operation is complete, the operator can perform the second stroke of the control rod to cause the desired ejection of the capillary-piston consumable. Nevertheless, this ejection operation is effected with the aid of the operator's only thumb by counteracting the return force of the second spring, which is necessarily substantial in order to contrast with the restoring force of the first spring, and thus to be able to perform its function of delivering a sensory signal to the operator at the end of the first race. The high stiffness of the second spring thus makes the pipette perfectible from an ergonomic point of view, especially since this disadvantage also occurs during the above-described operation of opening the clamp, before the introduction of the piston.

At least some of the disadvantages mentioned above are identical or similar on current pipetting systems of the type positive displacement machines.

In addition, another disadvantage of the ejection system provided on positive displacement pipettes known to date is that it is based on a design far removed from that of the ejection system for conventional pipettes with displacement of air. The As operators are generally more used to using such displacement pipettes, there is a need to harmonize the design of the positive displacement pipette ejection system.

STATEMENT OF THE INVENTION

The invention therefore aims to at least partially overcome the disadvantages mentioned above, relating to the achievements of the prior art.

To this end, the subject of the invention is a lower part of a positive displacement pipetting system, comprising a body slidably housing a device for gripping the upper end of a piston belonging to a capillary-piston assembly whose capillary is intended to be fitted on a tip of the body. According to the invention, the lower part also comprises means for ejecting the capillary-piston assembly arranged externally with respect to said body and slidably mounted relative thereto along a longitudinal axis of the pipetting system, so as to be able to cooperate with said capillary for ejection. In addition, the lower part is designed so that a relative rotation between the ejection means and the gripping device, along the longitudinal axis of the pipetting system, causes the passage of the gripping device of an open configuration allowing releasing the upper end of the piston, a closed configuration for retaining this end, and / or the transition from the closed configuration to the open configuration.

The invention is remarkable in that it is based on a design for dissociating the elements providing the control function of the pipette from those ensuring the ejection of the capillary-piston consumable. More specifically, the invention provides that the ejection of the consumable is effected by dedicated ejection means surrounding the body of the lower part, in the manner of similar ejection means frequently encountered on the displacement pipettes . Therefore, unlike the embodiments of the prior art where the ejection means integrate the control rod, the risk of accidental ejection of the consumable by the same control rod are advantageously reduced to nothing.

Thus, during the manipulation of the pipette, the operator can operate the control rod without worrying about the risks of such a loss, which overall makes it possible to improve the ergonomics, the reproducibility of the samples, and the productivity. This is also the case when the invention applies to a PLC for positive displacement sampling.

In addition, the force to be delivered to ensure the ejection of the consumable can be much lower than that previously required to counter the restoring force of the spring with high stiffness, since it is no longer necessary to provide a high differential stiffness springs for producing a sensory signal for the operator. In addition, the low support force required to unstick the capillary from the pipette tip has no impact on the risk of accidental loss of capillary-piston consumable, as explained above. This force is also low because of the possibility of bringing the gripper into open configuration during the ejection of the piston-capillary assembly. Therefore, during the ejection which is carried out in the manner of a conventional ejection pipette air displacement, there is no need to counter the frictional force between the upper end of the piston and the clamp. This results in better ergonomics for the operator.

The relative rotation between the ejection means and the gripping device can be effected in different ways. A solution of manually rotating the ejection means may be considered, but automation of this movement is preferred. This automation is preferably effected by mechanical means of motion converters, as will be exemplified hereinafter. To do this, mechanical links of the ramp / pin type are preferably located on the lower part of the pipetting system according to the invention.

Preferably, the gripping device comprises a movable jaw between a first position bringing the device in closed configuration and a second position bringing the device in open configuration, the jaw comprising one of the two elements among a first pin passing through said body and a first ramp cooperating with the first pin, the other of the two elements being provided on said means ejection. In addition, the passage of the jaw from the first position to the second position, and vice versa, is effected by relative movement of the first pin along said first ramp.

Preferably, said gripping device is equipped with elastic return means reminding the movable jaw in its first position or in its second position.

Preferably, the gripping device comprises one of two elements among a second pin passing through said body and a second ramp cooperating with the second pin, the other of the two elements being provided on said ejection means. In addition, the lower part of the pipetting system is designed so that during a downward movement of the gripping device, the latter moves from its open configuration to its closed configuration by relative rotation between the ejection means and the gripping device caused by the relative displacement of the second pin along said second ramp. It is preferentially this relative rotation which causes said bit to move from its first position to its second position.

Preferably, the second ramp is designed so that after the passage in the closed configuration of the gripping device, this closed configuration is retained during a recovery of the gripping device. A pipetting sequence can then be carried out using conventional means for controlling the pipette.

Preferably, said body comprises one of two elements among a third pin and a third ramp cooperating with the third pin, the other of the two elements being provided on said ejection means. In addition, the lower part of the pipetting system is designed so that during a downward movement of the ejection means, said gripping device is brought from the closed configuration to the open configuration by rotating the means for dispensing. ejection relative to said body, caused by relative movement of the third pin along said third ramp. Also, this makes it possible to obtain a helical displacement of the ejection means by applying to them a simple translation movement downwards. The capillary thrust and the release of the piston are therefore performed simultaneously for a perfectly optimized ergonomics.

Preferably, the third ramp is designed so that after the passage in open configuration of the gripping device, this open configuration is maintained during a recovery of the ejection means. Therefore, the gripping device advantageously remains in open configuration, ready to cooperate with a new capillary-piston assembly.

Preferably, the first, second and third ramps are provided on the inner surface of the ejection means. Alternatively, they could be placed, at least one of them, on the body and / or the gripping device.

Preferably, said ejection means comprise a ring surrounding the body and rotatably carrying an ejection sleeve also surrounding the body. It is thus this sheath that is intended to be pivotable relative to the gripping device, to bring it in open or closed configuration. In this regard, it is indicated that the aforementioned relative rotation is preferably performed by rotating the ejection means about the longitudinal axis of the pipetting system, keeping, along the same axis, the gripping device fixed in rotation. An inverse technical solution is however possible, without departing from the scope of the invention. Similarly, a mixed solution where the ejection means and the gripping device would rotate in opposite directions is also possible.

The invention also relates to a positive displacement pipetting system comprising a lower part as described above.

Preferably, it is a pipette, manual or motorized, comprising a high part forming a handle equipped with an ejection button connected to said ejection means. In this case, said ejection button is preferably separate from a button for controlling the movement of the piston.

Alternatively, the pipetting system may be an automaton.

1. (a) emmanchement du capillaire de l'ensemble capillaire-piston sur un embout du système de pipetage, et introduction de l'extrémité haute du piston de l'ensemble dans le dispositif de préhension lors de son déplacement jusqu'à une position basse, introduction au cours de laquelle il est opéré une rotation relative entre lesdits moyens d'éjection et le dispositif de préhension pour amener ce dernier de la configuration ouverte à la configuration fermée, afin de retenir l'extrémité haute du piston ;
2. (b) prélèvement et dispense d'un échantillon par actionnement d'une tige de commande reliée au dispositif de préhension ;
3. (c) éjection de l'ensemble capillaire-piston par déplacement vers le bas desdits moyens d'éjection poussant le capillaire, éjection au cours de laquelle il est opéré une rotation relative entre lesdits moyens d'éjection et le dispositif de préhension pour amener ce dernier de la configuration fermée à la configuration ouverte libérant l'extrémité haute du piston.

The invention also relates to a method of pipetting using a positive displacement pipetting system as described above, comprising the following successive steps:

1. (a) fitting the capillary of the capillary-piston assembly to a tip of the pipetting system, and introduction of the upper end of the piston of the assembly into the gripping device when it is moved to a low position, introduction during which there is a relative rotation between said ejection means and the gripping device to bring it from the open configuration to the closed configuration, to retain the upper end of the piston;
2. (b) sampling and dispensing a sample by actuating a control rod connected to the gripping device;
3. (c) ejection of the capillary-piston assembly by downward displacement of said ejection means pushing the capillary, ejection during which it is operated a relative rotation between said ejection means and the gripping device to bring this last from the closed configuration to the open configuration releasing the top end of the piston.

Preferably, for step (a), said relative rotation between said ejection means and the gripping device is performed automatically during the descent of the gripping device, and for step (c), said relative rotation between said ejection means and the gripping device is performed automatically during the descent of the ejection means. As mentioned above, if the desired automation can take any form deemed appropriate by those skilled in the art, it is preferably implemented by mechanical means of motion converters such as mechanical links of the ramp / pawn type or the like.

Other advantages and features of the invention will become apparent in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 représente une vue en perspective d'une pipette de prélèvement à déplacement positif, selon un mode de réalisation préféré de la présente invention ;
• la figure 2 représente une vue en coupe de la partie basse de la pipette montrée sur la figure précédente, avec la pipette se trouvant en configuration dépourvue d'ensemble capillaire-piston, et avec le bouton de commande en position haute ;
• la figure 3 représente une vue coupée transversalement montrant des liaisons rampe/pion spécifiques à la présente invention ;
• la figure 4 est une vue schématique de côté des moyens d'éjection, montrant des liaisons rampe/pion spécifiques à la présente invention ; et
• les figures 5a à 8d, issues des figures 2 à 4, montrent la pipette dans différentes configurations au cours d'un cycle de pipetage.

This description will be made with reference to the appended drawings among which;

• the figure 1 is a perspective view of a positive displacement sampling pipette, according to a preferred embodiment of the present invention;
• the figure 2 represents a sectional view of the lower part of the pipette shown in the previous figure, with the pipette being in a configuration devoid of a capillary-piston assembly, and with the control knob in the up position;
• the figure 3 is a cross-sectional view showing ramp / pawn links specific to the present invention;
• the figure 4 is a schematic side view of the ejection means, showing ramp / pin links specific to the present invention; and
• the Figures 5a to 8d , resulting from Figures 2 to 4 , show the pipette in different configurations during a pipetting cycle.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

With reference first to the figure 1 , there is shown a positive displacement sampling pipette 1, according to a preferred embodiment of the present invention.

Throughout the following description, the terms "high" and "low" are to be considered with the pipette held vertically, in the pipetting position or close to this same position.

The pipette 1 has an outer body whose upper part forms a handle 2 for the operator, and whose lower part 4 is tapered, ending down by a tip 6 on which a capillary is intended to be fitted. The lower part 4 is mounted preferably screwed on the handle body 2, by a threaded ring 5, so as to facilitate assembly / disassembly.

The pipette incorporates a control rod 8, slidably housed inside the outer pipette body. The rod 8 is arranged along the longitudinal axis 10 of the pipette. Its upper end protrudes upwardly from the handle body 2, and carries a control button 12 to be actuated by the thumb of an operator holding the body 2 with one of his hands. The rod 8 is slidably housed at through a volume adjustment screw to be taken (not shown). As shown in part on the figure 2 , the rod 8 may include a housing 11 of stroke reduction, to facilitate the movement of the rod to the operator.

In known manner, the rotation of the control rod 8 by its knob 12 makes it possible to move the adjusting screw relative to the outer pipette body along the axis 10, and thus causes a modification of the volume of the sample intended for to be taken.

The lower end of the control rod 8 is in axial abutment against a gripper-shaped gripper 20 slidably mounted in a bore 18 of the hollow body 19 of the lower part incorporating the tip 6 at its lower end.

As is visible on the figure 2 , the clamp 20 comprises a body 24 of contact with the lower end 16 of the control rod, extended downwards by one or more fixed jaws, also called jaws. As an indicative example, there is provided a fixed jaw 25 made in one piece with the clamp body 24, this fixed jaw extending for example on an angular sector of the order of 270 ° or more. In addition, the clamp 20 comprises a movable jaw 26 pivotally mounted on the body 24, along an axis 27 orthogonal to the axis 10. As will be detailed below, by pivoting along the axis 27, the movable jaw 26 can adopt a first position bringing the clamp into a closed configuration, and a second position shown on the figure 2 bringing the clamp into open configuration.

Elastic return means 32 make it possible to return the movable jaw 26 to its first position ensuring clamping of the clamp 20. To this end, the elastic return means urge the jaws / jaws 25, 26 radially inwards, preferably by surrounding these same jaws. It can then be a spring 32 of annular overall shape, whose diameter can be increased when it is stressed radially outwardly. In the example shown on the figure 2 the spring 32 takes the form of a spiral spring enclosing the outer surface of the jaws 25,26.

In addition, each jaw 25, 26 has a chamfered end so as to facilitate the insertion of the piston, as will be explained below.

In addition, the clamp body 24 has a first shoulder 38 facing downwards, facing and at a distance from a shoulder 40 formed on the lower part 4, near the endpiece 6. A return spring 42 is housed in support between these two shoulders 38, 40, to form a return spring in the upper position of the clamp 20 and the control rod located in abutment, in its extension. The restoring force developed by this compression spring 42 effectively drives the control rod 8 to adopt its high position relative to the outer body, a conventional high abutment (not shown) being provided for this purpose on the same outer body.

The clamp 20 comprises a second shoulder 44, also facing downwards and away from the shoulder 40. The second shoulder 44 is located further down and radially inwardly relative to the first shoulder 38. It is thus surrounded by the spring 42. As will be described below, it is intended to constitute a lower stop for the clamp 20 and the control rod 8 resting on the same clamp. In the high position shown on the figure 2 , the clamp 20 is located outside the tip 6, away from it, upwards.

One of the peculiarities of the present invention lies in the presence of ejection means 46 of a capillary-piston assembly, mounted externally around the hollow body 19, and sliding relative to the latter in the direction of the axis 10.

These means 46 comprise an intermediate ring 47 surrounding the hollow body 19 of the lower part, this ring bearing rotatively downwardly, an ejection sleeve 49 also surrounding the body 19. The sleeve has a low end 51 arranged to near the tip 6 and intended to press the capillary fitted to proceed to its ejection.

The intermediate ring 47 is carried by an upper arm 52, which extends upwardly possibly through an orifice 54 of the handle 2, to an upper end fixed to an ejection button 48. This button 48 is arranged in the upper part of the pipette, near the main control button 12, but separate from the latter. It is also intended to be simply operated by the thumb of an operator holding the body 2 with one of his hands.

With reference jointly to Figures 2 to 4 it is shown different elements specific to the present invention. Firstly, the movable jaw 26 extends upwards, presenting a first pin 54 oriented radially outwards and passing through a slot 56 formed in the hollow body 19. The pin 54 bears on a first ramp 58 provided on the inner surface of the sleeve 49. The ramp 58 is a circumferential ramp, the receiving surface of the pin 54 has, with reference to the axis 10, an evolutionary radial gap. Indeed, as this is best seen on the figure 3 , the ramp 58 has in particular a zone 58a close to the axis 10, a zone 58b remote from this same axis, and a transition zone 58c between the zones 58a, 58b. These areas 58a, 58c, 58b follow one another in the circumferential direction.

When the pin 54 is in the second position shown on the figures 2 and 3 it contacts the close zone 58a of the ramp 58, which causes the lower end of the jaw 26 to be located further away from the fixed jaw 25, and thus to place the clamp in open configuration in which the piston of a set capillary-piston can easily penetrate. The adoption of this second position of the movable jaw 26 is tolerated by the deformation of the spring 32 enclosing the jaws.

The mechanical connection formed by the pin 54 and the ramp 58 is such that when the pin moves relative to the ramp in the direction of the remote zone 58b, this causes pivoting of the movable jaw 26 along the axis 27, under the action of the restoring force of the spring 32. The movable jaw 26 thus moves from its second position to its first position by relative movement of the pin 54 along the ramp 58, and vice versa. In the first position to be described below, the jaws 25, 26 close place the clamp 20 in a closed configuration ensuring the maintenance by friction of the piston in the clamp.

In addition, there is provided another mechanical connection comprising a second pin 60 projecting radially outwardly from the clamp body 24, and passing through a slot 64 formed in the hollow body 19. A second ramp 62 is associated with the pin 60. The pin 60 is supported on this second ramp 62 also provided on the inner surface of the sleeve 49.

The ramp 62 has a complex shape which will be detailed with reference to the figure 4 . First, it has a generally U-shaped shape, with a first flank 62a oriented parallel to the axis 10, and practiced in the thickness of the hollow body 19. In the lower part, the first flank 62a is continued by a zone 62b, which is both inclined axially and circumferentially. It is an area comparable to a portion of helical ramp. Optionally, at the output of this actuating zone 62b, the ramp 62 comprises a retaining zone 62c extending axially downwards and having a width substantially corresponding to that of the pin 60. Next, the second axial flank is provided. 62d, parallel to the first.

When the control knob is in the up position, as the clamp 20 in open configuration as shown on the Figures 2 to 4 , the peg 60 is supported on an upper part of the first flank 62a.

Furthermore, there is provided another mechanical connection comprising a third pin 68 projecting radially outwardly from the hollow body 19. A third ramp 70 is associated with the pin 68. The pin 68 bears on this third ramp 70 also provided on the inner surface of the sleeve 49.

The ramp 70 has a complex shape which will be detailed with reference to the figure 4 . First, it has a generally U-shaped, with a first side 70a oriented parallel to the axis 10, and made in the thickness of the hollow body 19. In the lower part, the first side 70a is connected to a bottom 70b oriented transversely in a plane orthogonal to the axis 10. Opposite the first flank 70a is a second flank having a lower actuating portion 70c, which is both inclined axially and circumferentially. Its circumferential inclination is made in a direction opposite to that of the inclination of the actuating zone 62b of the second ramp. This is also an area comparable to a portion of helical ramp. The second flank then extends with a dead zone 70d symmetrical with the actuating zone 70c, relative to a transverse plane of the pipette. The dead zone makes it easier to insert the pin 68 during assembly of the pipette.

Referring now to Figures 5a to 8d , it will be described the operation of the pipette 1.

First of all with reference to Figures 5a to 5d , the operator gripping the pipette by the handle 2 engages the tip 6 in a capillary 80 of a consumable capillary-piston assembly 84, preferably arranged in a housing, also called "rack". By exerting a vertical downward pressure on the pipette, it obtains the fitting of the capillary 80 on the tip 6, in the manner of fitting a capillary or a conventional cone on the tip of a nozzle. classic pipette with air displacement.

Then, the operator presses the control button 12 to bring the control rod 8 and the clamp 20 to the low position. This displacement results in a movement of the second pin 60 along the first flank 62a of the second ramp 62, to the bottom of this first flank. During this first phase of descent of the clamp, the angular position of the sleeve 49 relative to the body 19 and the clamp 20 remains preserved. The movable jaw 26 thus undergoes no displacement along its pivot axis 27, its second position being maintained by the support of the pin 54 on the close zone 58a of the first ramp 58. The relative position of the third pin 68 on the ramp 70 remains unchanged, namely that the pin 68 is in abutment against the bottom 70b and the first flank 70a. During this first phase of descent of the clamp authorized by the compression of the spring 42, the upper end 86 of the piston 82 has begun its introduction between the spaced jaws 25, 26.

When the movement of the rod 8 and the clamp 20 is continued downwards, always against the spring 42, the second pin 60 bears on the operating zone 62b of the second ramp 62, as is shown on Figures 6a to 6d . The support caused by the relative displacement of the pin 60 along the ramp zone 62b pushes the sleeve 49 to rotate in the direction of the arrow 77 of the figure 6b . Also, during this second phase of descent of the clamp 20 during which the end of the introduction of the upper end 86 of the piston 82 into the clamp 20, it is also automatically created a rotation of the sleeve 49 according to the axis 10, which has the effect of bringing the clamp in closed configuration. Indeed, during this rotation of the sleeve 49, the clamp 20 remains fixed in rotation along the axis 10 but the pin 54 moves along the ramp 58 to access the remote zone 58b, while pivoting along its axis 27 under the effect of the spring 32. Also during this automatic rotation of the sleeve which remains fixed axially, the third pin 68 moves along the bottom 70b of the ramp, until it comes into contact with the bottom of the zone actuator 70c.

In the end position shown on the Figures 6a to 6d , the closed gripper 20 gripping the piston 82 is in low abutment on the lower body 19, by contact between the shoulders 44, 40.

At the end of this step, the piston is in the lower abutment position in the capillary. Thus, to simplify the sampling process, the control rod 8 is preferably kept in the down position until the sample is taken, during which the control rod rises with the piston to create the suction of the liquid.

During this rise of the piston and the pliers schematically on the Figures 7a to 7d , the closed configuration of this clamp 20 is of course retained to maintain the piston by friction. During the ascent, the second pin 60 then moves along the second flank 62d of the ramp 62, while the relative position of the third pin 68 and the third ramp 70 remains unchanged. There is therefore no relative rotational movement between the sleeve 49 and the clamp 20 or the body 19.

It is then the dispensing of the sampled liquid which is carried out, by displacement of the control rod via its knob 12, in a manner identical to that performed for the gripping of the piston, but with the movable jaw 26 maintained in its first position. piston tightening. Indeed, the stroke is the same, bringing the control rod 8 in the low position to the contact between the shoulders 44, 40.

Finally, the consumable assembly 84 is ejected by means of the ejection means 46 actuated by the ejection button 48. This ejection step is schematized on the Figures 8a to 8d .

The axial support on the ejection button 48 drives the ring 47 and the sleeve 49 to slide down along the axis 10. But during this descent of the ejection means, the support caused by the relative displacement of the pin 68 along the actuating zone 70c of the third ramp 70 pushes the sleeve 49 to rotate in the direction of the arrow 79 of the figure 8b , that is to say in a direction opposite to that observed on the figure 6b when placing the capillary-piston assembly on the pipette. Also, during this phase of descent ejection means, it is automatically created a rotation of the sleeve 49 along the axis 10, which has the effect of bringing the clamp in open configuration. Indeed, during this rotation of the sleeve 49 which is in fact a helical movement along the axis 10, the clamp 20 and the body 19 remain fixed in rotation along the axis 10 but the pin 54 moves along the ramp 58 to access to the close zone 58a of the first ramp, while pivoting along its axis 27 by counteracting the return force of the spring 32. Again during this downward movement of the sleeve 49 which bears with its lower end 51 on the capillary 80 for its ejection, the second pin 60 moves circumferentially to reach again the first flank 62a, at an upper part thereof.

In other words, during the helical movement of the sheath 49, simultaneous creation of a thrust of the capillary via the lower end 51 of the sheath, and an opening of the clamp 20 releasing the upper end 86 of the piston 82. assembly 84 can thus be ejected easily, in a clever way specific to the present invention.

Finally, it is indicated that during the raising of the ejection means, the open configuration of the clamp 20 is of course kept in order to keep the pipette ready for future use. During this ascent, the third pin 68 moves along the first edge 70a that it has already contacted at the end of the ejection operation, because of the small width between the upper end of the actuating zone 70c and the first flank 70a. Once the ejection means returned to the high position, the pin 68 is found again at the junction between the flank 70a and the bottom 70b. Moreover, during the ascent of the ejection means 46, the relative position of the second pin 60 and the second ramp 62 remains unchanged. There is therefore no relative rotational movement between the sleeve 49 and the clamp 20 or the body 19.

Of course, various modifications may be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples.

Claims (15)

1. Bottom part (4) of a positive-displacement pipetting system (1), including a body (19) slideably housing a device (20) for gripping the top end (86) of a piston (82) belonging to a capillary-piston assembly (84) the capillary of which is intended to be fitted onto an end-fitting (6) of the body,
   characterized in that it also comprises means (46) for ejecting the capillary-piston assembly arranged externally with respect to said body (19) and slideably mounted relative to it according to a longitudinal axis (10) of the pipetting system, so as to be capable of cooperating with said capillary for ejection thereof,
   and in that the bottom part is also designed so that a relative rotation between the ejection means (46) and the gripping device (20), according to the longitudinal axis (10) of the pipetting system, causes the gripping device to pass from an open configuration enabling the top end (86) of the piston (82) to a closed configuration enabling said end to be retained, and/or to pass from the closed configuration to the open configuration.
2. Bottom part of pipetting system according to claim 1, characterized in that the gripping device (20) has a jaw (26) mobile between a first position bringing the device (20) into the closed configuration and a second position bringing the device into the open configuration, the mobile jaw (26) comprising one of the two elements among a first pin (54) passing through said body (19) and a first ramp (58) cooperating with said first pin, the other of the two elements being provided on said ejection means (46), and in that the passage of the mobile jaw (26) from the first position to the second position, and the reverse, is caused by a relative displacement of the first pin (54) along said first ramp (58).
3. Bottom part of pipetting system according to claim 2, characterized in that the gripping device (20) is equipped with resilient return means (32) returning the mobile jaw (26) to its first position or to its second position.
4. Bottom part of pipetting system according to any one of the previous claims, characterized in that the gripping device (20) comprises one of the two elements among a second pin (60) passing through said body (19) and a second ramp (62) cooperating with the second pin, the other of the two elements being provided on said ejection means (46), and in that the bottom part of the pipetting system is designed so that, during a downward displacement of the gripping device (20), the latter passes from its open configuration to its closed configuration by a relative rotation between the ejection means (46) and the gripping device (20) caused by the relative displacement of the second pin (60) along said second ramp (62).
5. Bottom part of pipetting system according to claim 4, characterized in that the second ramp (62) is designed so that, after the gripping device (20) passes into the closed configuration, this closed configuration is maintained as the gripping device rises.
6. Bottom part of pipetting system according to any one of the previous claims, characterized in that said body (19) comprises one of the two elements among a third pin (68) and a third ramp (70) cooperating with the third pin, the other of the two elements being provided on said ejection means (46), and in that the bottom part of the pipetting system is designed so that, during a downward displacement of the ejection means (46), said gripping device (20) is brought from the closed configuration to the open configuration by a rotation of the ejection means (46) relative to said body (19), caused by a relative displacement of the third pin (68) along said third ramp (70).
7. Bottom part of pipetting system according to claim 6, characterized in that the third ramp (70) is designed so that, after the gripping device (20) passes into the open configuration, this open configuration is maintained as the ejection means (46) rise.
8. Bottom part of pipetting system according to any one of the previous claims, characterized in that the first, second and third ramps (58, 62, 70) are provided on the interior surface of the ejection means (46).
9. Bottom part of pipetting system according to any one of the previous claims, characterized in that said ejection means (46) include a ring (47) surrounding the body (19) and rotatably bearing an ejection sheath (49) also surrounding the body (19).
10. Positive-displacement pipetting system (1) including a bottom part (4) according to any one of the previous claims.
11. Pipetting system according to claim 10, characterized in that it is a pipette (1), manual or powered, comprising a handle-forming top part (2) equipped with an ejection button (48) connected to said ejection means (46).
12. Pipetting system according to claim 11, characterized in that said ejection button (48) is distinct from a button (12) for controlling the displacement of the piston (82).
13. Pipetting system according to claim 10, characterized in that it is an automated system.
14. Pipetting method using a positive-displacement pipetting system (1) according to any one of claims 10 to 13, including the following successive steps:

    (a) fitting of the capillary (80) of the capillary-piston assembly (84) on the end-fitting of the pipetting system, and insertion of the top end (86) of the piston of the assembly into the gripping device (20) during the displacement thereof to a bottom position, during which insertion a relative rotation is performed between said ejection means (46) and the gripping device (20) in order to bring the latter from the open configuration to the closed configuration, so as to retain the top end of the piston;

    (b) collection and dispensing of a sample by actuation of a control rod (8) connected to the gripping device;

    (c) ejection of the capillary-piston assembly (84) by downward displacement of said ejection means (46) thrusting the capillary, during which ejection a relative rotation is performed between said ejection means (46) and the gripping device (20) in order to bring the latter from the closed configuration to the open configuration releasing the top end of the piston.
15. Method according to claim 14, characterized in that, for step (a), said relative rotation between said ejection means (46) and the gripping device (20) is performed automatically as the gripping device (20) descends, and in that, for step (c), said relative rotation between said ejection means (46) and the gripping device (20) is performed automatically as the ejection means (46) descend.

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