Pipette for sampling an extended range of volumes of liquid

Abstract

A pipette for sampling an extended range of volumes of liquid includes a fixed pipette body. An operating rod is movable in translation relative to the pipette body, along a longitudinal axis of the pipette. The pipette includes a suction chamber and a set of N concentric pistons, wherein N corresponds to an integer greater than or equal to 2. Each of the pistons contributes to delimiting the suction chamber. A coupling module couples the operating rod with the set of N concentric pistons. The module is configured in such a way as to be able to be brought into N distinct configurations in which it respectively couples the operating rod with 1, 2, . . . , N pistons.

Claims

1. A sampling pipette comprising: a pipette fixed body; a control rod extending within the pipette fixed body and translationally movable relative to the pipette body, along a longitudinal axis of the pipette fixed body; a suction chamber inside the pipette fixed body; a set of N concentric pistons in the pipette fixed body located along the longitudinal axis, N corresponding to an integer higher than or equal to two, each of the N pistons are movable along the longitudinal axis within said suction chamber; and a coupling module in the pipette fixed body coupling the control rod with the set of N concentric pistons, the coupling module is configured to have N distinct configurations in which the coupling module provides a respective coupling of the control rod to each of the respective N pistons.

2. The sampling pipette according to claim 1, wherein the coupling module comprises at least one piston attachment finger radially extending from the coupling module relative to the longitudinal axis, wherein at least one piston has an attachment slot extending circumferentially about the at least one piston, the attachment slot having an open end, and wherein the attachment finger is movable circumferentially in and out of the attachment slot.

3. The sampling pipette according to claim 1, wherein the coupling module comprises at least one piston attachment finger radially extending from the coupling module relative to the longitudinal axis, wherein at least one of N pistons has an attachment slot extending circumferentially about the at least one piston, the attachment slot having an and open end, and wherein the at least one piston attachment finger is movable circumferentially in and out of the attachment slot.

4. The sampling pipette according to claim 3 wherein the coupling rotary member includes two parts slidably mounted with respect to each other, along the longitudinal axis, and an expansion spring disposed between the two parts and configured to generate a strain to move the two parts away from one another.

5. The sampling pipette according to claim 4, wherein the coupling module includes a control rod extension translationally integral with the control rod, and said two parts of the coupling rotary member being a top part and a bottom part respectively, the bottom part being translationally movably mounted along the longitudinal axis, relative to the control rod extension.

6. The sampling pipette according to claim 3, wherein the coupling module further comprises a motion transforming body engaging the coupling rotary member wherein a relative translation movement between the motion transforming body and the coupling rotary member along the longitudinal axis simultaneously results in a relative rotation of the motion transforming body and the coupling rotary member, also along the longitudinal axis.

7. The sampling pipette according to claim 6, wherein the motion transforming body includes at least one first helical ramp and at least one second helical ramp, and the coupling rotary member comprises a follower roller, wherein the follower roller is configured to engage the at least one first ramp and cause the at least one first ramp to produce a rotation of the coupling rotary member along a first direction of rotation, and wherein the follower roller is configured to engage the at least one second ramp and cause the at least one second ramp to produce a rotation of the coupling rotary member along a second direction of rotation.

8. The sampling pipette according to claim 7, wherein the coupling rotary member is configured so that the rotation of the coupling rotary member along the first direction of rotation is caused by a first overstroke downwards of the control rod from a purge stroke end position, and the rotation of the coupling rotary member along the second direction of rotation is caused by a second overstroke upwards of the control rod from a top pipetting position of the control rod.

9. The sampling pipette according to claim 8, further comprising a first centering spring and a second centering spring, wherein the first overstroke acts against a strain generated by the first centering spring that repels the coupling rotary member upwardly relative to the motion transforming body, and the second overstroke acts against a strain generated by the second centering spring that repels the coupling rotary member downwardly relative to the motion transforming body.

10. The sampling pipette according to claim 1, further comprises a motor configured to move the control rod or the control rod is configured to be moved manually.

11. The sampling pipette according to claim 1, wherein the number N of pistons is higher than or equal to three.

12. The sampling pipette according to claim 1, wherein the sampling pipette has a volume range from 0.5 to 1,250 μl, or from 500 to 10,000 μl.

13. The sampling pipette according to claim 1, further comprising a control member for adjusting a volume to be sampled.

14. The sampling pipette according to claim 1, wherein the set of N concentric pistons includes an innermost piston that is permanently integral with the coupling module.

15. The sampling pipette according to claim 1, wherein the coupling module comprises at least one piston attachment finger radially extending from the coupling module relative to the longitudinal axis, wherein two pistons of the N pistons each have an attachment slot extending circumferentially about each respective piston, each attachment slot having an open end and a different circumferentially length from the respective other attachment slot, the two attachment slots radially face each other, and wherein the at least one attachment finger is circumferentially movable in and out of the two attachment slots.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) This description will be made with regard to the appending drawings in which:

(2) FIG. 1 represents a front view of a motor sampling pipette according to a preferred embodiment of the present invention;

(3) FIG. 2 is an axial cross-section view of a bottom part of the pipette shown in the previous figure;

(4) FIG. 3 is a perspective view of a piston coupling module implemented in the pipette shown in the previous figures;

(5) FIG. 4 is an axial cross-section view of the previous figure;

(6) FIG. 5 is cross-section view taken along line V-V of the previous figure;

(7) FIG. 6 is a perspective view of a bottom part of the coupling module shown in FIGS. 3 and 4, cooperating with the pistons of the pipette;

(8) FIGS. 7a to 7c depict pipetting operations with the coupling module in a first configuration;

(9) FIGS. 8a to 8c depict pipetting operations with the coupling module in a second configuration;

(10) FIGS. 9a to 9c depict pipetting operations with the coupling module in a third configuration;

(11) FIGS. 10a to 11b depict the coupling module switching from the first to the second configuration;

(12) FIGS. 12 to 13b depict the coupling module switching from the second to the third configuration;

(13) FIGS. 14a to 15b depict the coupling module switching from the third to the second configuration; and

(14) FIGS. 16a to 17b depict the coupling module switching from the second to the first configuration.

DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS

(15) In reference to FIGS. 1 to 5 first, a motor sampling pipette 1 is represented according to a preferred embodiment of the invention.

(16) Conventionally, this motor pipette 1 is intended to be held by an operator's hand who, using his/her thumb, is capable of actuating a control knob of the pipette to generate dispensing a liquid which has been sucked beforehand.

(17) More precisely, the single-channel pipette 1 comprises a handle 6 forming the upper body of the pipette, and above which the pipetting control button 3 is located, the upper part of which is intended to undergo the operator's thumb pressure. By way of indicating purposes, it is noted that an electronic display screen 4 is provided on the handle 6, as well as control members 8 such as knobs or buttons, and in particular a control member for adjusting the volume to be sampled.

(18) The top part of the pipette is also provided with an electronic control unit 10 and a motor 11, the latter being preferentially a direct current motor controlled by the unit 10.

(19) The output shaft 13 of the motor 11 is mechanically coupled to a device 15 for translating a control rod 12 of the pipette, along a longitudinal axis 9 of the pipette also corresponding to the longitudinal direction of the same. It is noted that most of the elements making up the pipette are of revolutionary shapes, and centred on this axis 9.

(20) Under the handle 6, the pipette 1 includes a removable bottom part 14, which downwardly terminates with a cone-carrying tip 16 accommodating a consumable 18, also called a sampling cone.

(21) A cone ejector 20 opens downwardly of the handle 6. Conventionally, the ejector 20 can be moved relative to the handle 6 and the bottom part 14, both forming a fixed body 22 of the pipette.

(22) One of the features of the invention lies in the fact that the pipette is equipped with several concentric pistons, here three pistons referenced 24a, 24b, 24c. The number N of pistons could however be higher or lower than 3, without departing from the scope of the invention.

(23) The three pistons are housed in the bottom part 14, and centred on the longitudinal axis 9. The first piston 24a, located inside, has a circular shaped cylindrical cross-section. The second piston 24b has an annular transverse cross-section, surrounding the first piston 24. The top end 24b′ of the second piston 24b defines an upwardly open axial housing 26, and the bottom of which is equipped with an O-ring 28 through which the first piston 24a passes. However, usually for the second piston 24b, a small radial clearance is provided between both pistons 24a, 24b, such that air can penetrate therethrough. It is indicated that throughout the description, the terms “top” and “bottom” are to be considered with respect to the pipette maintained in the operator's hand, with an orientation such as that assumed during pipetting operations, that is with the control knob 3 upwardly oriented.

(24) Analogously to that set out above, the top end 24c′ of the third piston 24c defines an upwardly open axial housing 30, and the bottom of which is equipped with an O-ring 32 through which the second piston 24b passes. However, usually for the third piston 24c, a small radial clearance is provided between both pistons 24b, 24c, such that air can penetrate therethrough.

(25) The third piston 24c has a bottom end equipped with a lip seal 40 snuggly fitting the internal surface of the fixed body 22.

(26) Each of the second and third pistons 24b, 24c has lugs 34 outwardly radially extending and slidably mounted in vertical internal grooves 36 of the fixed body 22, as is visible in FIG. 4. This enables the rotation of the pistons to be blocked relative to the fixed body 22 of the pipette.

(27) The pistons participate with their lower ends in delimiting a single suction chamber 42, the bottom part of which communicates with a channel 44 passing through the cone-carrier 16.

(28) By way of indicating example, the pipette is intended to enable liquid to be sampled in a volume range from 0.5 to 1,250 μl, or in a volume range from 500 to 10,000 μl. In the first case for example, a first piston 24a is provided, the intrinsic sampling capacity of which is in the order of 50 μl, and a second piston 24b is provided which, when associated with the first piston 24a, has together an intrinsic sampling capacity in the order of 350 μl, and finally a third piston 24c is provided which, when associated with the first and second pistons 24a, 24b, has an intrinsic sampling capacity in the order of 1,250 μl.

(29) Depending on the desired volume, adjusted by the operator via the dedicated control member on the pipette, the control unit 10 is capable of commanding switching ON either: the first piston 24a only; the first and second pistons 24a, 24b; the first, second and third pistons 24a-24c.

(30) For this, the pipette 1 is equipped with a coupling module 50 specific to the invention, enabling each of the pistons to be coupled and uncoupled with the control rod 12. More precisely, the module 50 is configured so as to be able to be brought into three distinct configurations in which it provides coupling of the control rod 12 with the first piston 24a only, the first and second pistons 24a, 24b, and finally the first, second and third pistons 24a, 24c respectively.

(31) More specifically in reference to FIGS. 3 and 4, the coupling module 50 will now be described in more details.

(32) First, the module 50 includes a control rod extension 52 translationally integral with the control rod 12, and downwardly extending from the same rod. Preferably, the extension 52 is mounted screwed at its top end to the bottom end of the control rod 12.

(33) The bottom end of the extension 52, centred on the axis 9, fixedly and permanently carries the first piston 24a, a screwed, glued connection or else, being for example provided between their respective ends.

(34) Further, the module 50 includes a coupling rotary member 56, arranged about the control rod extension 52. Preferably, this member 56 is made using two parts slidably mounted with respect to one another, along the axis 9. There is first a top part 56a translationally fixed with respect to the rod 12 and its extension 52, but rotatably movable relative to the same, along the axis 9. There is then a bottom part 56b rotatably coupled to the top part 56a, for example through a key 60.

(35) An expansion spring 62 is arranged between both parts 56a, 56b, so as to generate a strain tending to move them away from one another. This expansion spring 62 presses against an internal pressing surface of the bottom part 56b, and a ring for coupling the upper ends of the top part 56a and the extension 52.

(36) The bottom part 56b is thus translationally movably mounted along the axis 9, relative to the extension 52 and to the control rod 12. It is additionally equipped, at its bottom end, with at least one piston attachment finger 64, preferably two diametrically opposite fingers as is shown in FIG. 3.

(37) Each attachment finger 64 radially outwardly extends from the bottom part 56b. As will be described hereinafter, the angular position of these fingers 64 conditions the number of pistons coupled to the module 50.

(38) To vary the angular position of the fingers 64, the coupling module 50 further includes a motion transforming body 66, for transforming a translational motion into a rotational motion along the same axis 9. Indeed, this body 66 cooperates with the top part 56a of the coupling rotary member 56 such that a relative translation movement between both of them along the axis 9 simultaneously results in a relative rotation between them along the same axis. The aim is therefore to obtain a helical motion of the coupling rotary member 56, which is made possible thanks to ramps provided on the body 66 as well as follower rollers carried by the rotary member 56.

(39) More precisely, the member 56 is equipped with two follower rollers 68 arranged in a diametrically opposite way, and rotatably mounted along a same transverse axis 76 orthogonal to the axis 9. A first helical ramp 70a located inside the body 66, as well as a second helical ramp 70b also located inside the body 66, facing the first ramp, are associated with each follower roller 68. The design is such that when each follower roller 68 cooperates with its associated first ramp 70a, it enables the rotation of the rotary member 56 to be caused along the first direction of rotation 72a about the axis 9. Reversely, when it cooperates with its associated second ramp 70b, it enables the rotation of the rotary member 56 to be caused along a second direction or rotation 72b opposite to the first direction.

(40) It is additionally noted that each follower roller 68 is carried by a rotational support pin 74 centred on the axis 76, this pin opening into a radial opening 76 of the motion transforming body 66.

(41) The axial positioning of the coupling rotary member 56 with respect to the body 66 is ensured by two compression springs, that is a first centring spring 80a tending to repel upwardly the member 56 relative to the body 66, and a second centring spring 80b tending to repel downwardly the coupling rotary member relative to the motion transforming body 66.

(42) For this, the first spring 80a is housed inside the body 66 between a bottom end thereof and a shoulder 82 located at the top end of the rotary member 66, whereas the second spring 80b is housed inside the body 66 between a top end of the same and the same shoulder 82. It is additionally noted that it is on this shoulder that the follower rollers 68 are preferentially mounted, via the pins 74.

(43) In reference now to FIG. 6, in combination with FIGS. 3 and 4, the cooperation between the coupling module 50 and the first and second pistons 24b, 24c will now be described, given that the first piston 24a remains permanently integral with this coupling module 50.

(44) At its top end 24b′, the second piston 24b has two diametrically opposite attachment slots 84b (a single one being visible in FIG. 6). Each slot 84b is circumferentially oriented, open in the same direction at one of its ends, and has a slot bottom at the opposite end. These slots 84b, for cooperating with the fingers 64 as lugs, are thus defined by notches 86b that would be considered as those of a bayonet connection.

(45) Analogously, at its top end 24c′, the third piston 24c has two diametrically opposite attachment slots 84c (a single one being visible in FIG. 6). Each slot 84c is also circumferentially oriented, open in the same direction at one of its ends, and has a slot bottom at the opposite end. These slots 84c, also for cooperating with the fingers 64 as lugs, are defined by notches 86c that could also be considered as those of a bayonet connection.

(46) The slots 84b, 84c are gathered by pairs. For a same pair of slots 84b, 84c as that visible in FIG. 6, these are radially facing each other. In other words, they are considered as superimposed along the radial direction, by only partially covering each other along the circumferential direction. Indeed, both slots 84b, 84c of a same pair have different circumferential lengths, while having their slot bottoms aligned along the radial direction. Consequently, in the preferred embodiment which is described and represented in the figures, this implies that each notch 86b provided on the second piston 24b and delimiting the slot 84b, is longer than the notch 86c provided on the third piston 24c and delimiting the slot 84c.

(47) The width of the slots 84b, 84c is preferentially identical, and provided such that the attachment fingers 64 can be circumferentially moved in and out these slots. Preferably, the slot width is slightly higher than the diameter of the fingers.

(48) With this configuration, the number of pistons coupled to the bottom part 56b of the module 50 thus depends on the relative angular position between each finger 64 and its associated pair of slots 84b, 84c. FIG. 6 does depict this principle, since in a first configuration of the module 50 which is represented with the finger 64 in solid line, the same finger 64 assumes an angular position such that it is located outside the two slots 84b, 84c. In this first configuration, both pistons 24b, 24c are not coupled to each other, only the first piston remaining integral with the module 50. This first configuration is for example assumed by the control unit for pipetting volumes being in a range from 0.5 to 30 μl.

(49) In a second configuration of the module 50, represented with the finger 64 in dotted line in the middle of FIG. 6, each finger 64 assumes an angular position such that it is located in the slot 84b, but outside the slot 84c. The cooperation between the finger 64 and the notch 86b is related to a bayonet connection. For example, an angular offset of 20 to 25° is provided between the position of the finger 64 of the first configuration, and that of the second configuration. In the same, both pistons 24a, 24b are therefore coupled to the module 50, but not the third piston 24c. This second configuration is for example assumed by the control unit for pipetting volumes being in a range from 30 to 300 μl.

(50) In a third configuration of the module 50, represented with the finger 64 in dotted line in FIG. 6, the finger 64 assumes an angular position such that it is located in the slots 84b, 84c, close to or in contact with the slot bottoms. The cooperation between the finger 64 and the notches 86b, 86c is related to bayonet connections. For example, an angular offset of 20 to 25° is provided between the position of the finger 64 of the second configuration, and that of the third configuration. In the same, the three pistons 24a-24c are therefore coupled to the module 50. This second configuration is for example assumed by the control unit for pipetting volumes being in a range from 300 to 1,250 μl.

(51) In reference now to FIGS. 7a to 7c, the operation of the pipette 1 will now be described when its coupling module 50 is in the first configuration, that is with only its first internal piston 24a coupled to this module.

(52) FIG. 7a shows the pipette 1 with its control rod in the top pipetting position, for example in a suction stroke end. The piston 24a coupled to the module 50 is thus in its topmost position relative to the fixed body 22 of the pipette. As regards the other two pistons 24b, 24c, they are in an inactive position abutting down against the fixed body 22. At this stage, the follower rollers 68 are substantially centred with respect to the motion transforming body 66, also in a top position.

(53) Dispensing the sucked liquid is then controlled by the control knob, which causes actuation of the motor resulting in the control rod 12 to be downwardly moved. During this dispensing stroke, the downward motion of the rod 12 drives the module 50 which therefore also slides along the fixed body 22. As regards the pistons 24b, 24c, they remain stationary, unlike the first piston 24a which moves down. The state of the pipette at the dispensing stroke end is represented in FIG. 7b, whereas the continuing moving down of the rod 12 results in performing a purge stroke, the final state of which is represented in FIG. 7c.

(54) In reference now to FIGS. 8a to 8c, the operation of the pipette 1 will be described when its coupling module 50 is in the second configuration, that is with only its first and second pistons 24a, 24b coupled to this module.

(55) FIG. 8 shows the pipette 1 with its control rod in the top pipetting position, for example at the suction stroke end. The pistons 24a, 24b coupled to the module 50 are in their topmost position relative to the fixed body 22 of the pipette. During pipetting, the relative axial position of both these pistons remains unchanged. As regards the third piston 24c, it remains in an inactive position abutting down against the fixed body 22. At this stage, the follower rollers 68 are substantially centred with respect to the motion transforming body 66, also in a top position.

(56) Dispensing the sucked liquid is then controlled by the control knob, which causes actuation of the motor resulting in the control rod 12 being downwardly moved. During this dispensing stroke, the downward motion of the rod 12 drives the module 50 which therefore also slides along the fixed body 22. The pistons 24c remains stationary, unlike the pistons 24a, 24b which simultaneously move down. The state of the pipette at the dispensing stroke end is represented in FIG. 8b, whereas the continuing moving down of the rod 12 results in performing a purge stroke, the final state of which is represented in FIG. 8c.

(57) In reference now to FIGS. 9a to 9c, the operation of the pipette 1 will be described when its coupling module 50 is in the third configuration, that is with all its pistons 24a-24c, coupled to this module.

(58) FIG. 9a shows the pipette 1 with its control rod in the top pipetting position, for example at the suction stroke end. The pistons 24a-24c coupled to the module 50 are in their topmost position relative to the fixed body 22 of the pipette. During pipetting, the relative axial position of these three pistons remains unchanged. At this stage, the follower rollers 68 are substantially centred with respect to the motion transforming body 66, also in a top position. As in the other two configurations, the position of the rollers 68 within the module is not caused to change during pipetting.

(59) Dispensing the sucked liquid is then controlled by the control knob, which causes actuation of the motor resulting in the control rod 12 to be downwardly moved. During this dispensing stroke, the downward motion of the rod 12 drives the module 50 which therefore also slides along the fixed body 22. The three pistons 24a-24c then simultaneously move down, pushed by the rod 12 and the module 50. The state of the pipette at the dispensing stroke end is represented in FIG. 9b, whereas the continuing moving down of the rod 12 results in performing a purge stroke, the final state of which is represented in FIG. 9c.

(60) FIGS. 10a to 10c and FIGS. 11a and 11b depict an operation aiming at switching from the first configuration to the second configuration of the module 50. For this, a first overstroke is commanded by the control unit, downward from the purge stroke end position as shown in FIG. 7c.

(61) The body 66 first abuts down against the fixed body 22. As the first overstroke continues, the top part 56a of the rotary member 56 is rotated because of the follower rollers 68 pressing against their ramps 70a. This helical motion is transmitted to the bottom part 56b, as well as to its attachment fingers 64. It is made against the return strain generated by the first centring spring 80a, by compressing the same. During this motion, the fingers 64 of the bottom part 56b also axially abut down against the top ends 24b′, 24c′ of the pistons 24b, 24c, this state corresponding to that represented in FIGS. 10a and 11a. Then, the first overstroke is continued and the top part 56a continues to be helically driven, whereas the bottom part 56b only undergoes a rotation along the axis 9 in the first direction 72a, since it is translationally blocked. The relative translational motion between both parts 56a, 56b is made against the return strain generated by the expansion spring 62, by compressing the same.

(62) During this rotation the angular extent of which is perfectly controlled because it directly depends on the extent of the axial overstroke of the control rod 12, the attachment fingers 64 penetrate the slots 84b. However, this angular movement of the fingers 64, for example in the order of 22.5°, is not sufficient for them to penetrate the slot 84c. The insertion of the fingers 64 into the slots 84b causes the second piston 24b to be coupled with the module 50. This mechanical coupling state is represented in FIGS. 10b and 11b.

(63) Once the coupling is made, the control unit of the pipette commands the rod 12 to be lifted back to the purge end position, which results in simultaneously lifting back the first and second pistons 24a, 24b, as is shown in FIG. 10c. As regards the third piston 24c, it remains in a fixed position.

(64) Then, pipetting operations can be commanded conventionally, for volumes corresponding to the range associated with all of the two pistons 24a, 24b.

(65) FIGS. 12 to 12c and FIGS. 13a and 13b depict an operation aiming at switching from the second configuration to the third configuration of the module 50. For this, another first overstroke with a larger amplitude than the previous one in commanded by the control unit, downwardly from the purge stroke end position as shown in FIG. 12.

(66) The body 66 first abuts down against the fixed body 22. As the first overstroke is continued, the top part 56a of the rotary member 56 is rotated because the follower rollers 68 press against their ramps 70a. This helical motion is transmitted to the bottom part 56b, as well as to its attachment fingers 64. During this motion, the fingers 64 of the bottom part 56b then axially abut down against the top end 24c′ of the piston 24c, this state corresponding to that represented in FIGS. 12a and 13a.

(67) Then, the first overstroke is continued and the top part 56a continues to be helically driven downwardly, whereas the bottom part 56b only undergoes a rotation along the axis 9 in the first direction 72a, since it is translationally blocked. During this rotation the angular extent of which is perfectly controlled because it directly depends on the extent of the axial overstroke of the control rod 12, the attachment fingers 64 penetrate the slots 84c. This angular movement of the fingers 64 is for example in the order of 22.5°, and sufficient to come against or in the proximity of the bottom of the slots 84b, 84c. The insertion of the fingers 64 into the slots 84c causes the third piston 24b to be coupled with the module 50. This mechanical coupling state is represented in FIGS. 12b and 13b.

(68) Once the coupling is made, the control unit of the pipette commands the rod 12 to be lifted back to the purge end position, which results in simultaneously lifting back the three pistons 24a-24c, as is shown in FIG. 12c. Then, pipetting operations can be commanded conventionally, for volumes corresponding to the range associated with all of the three pistons 24a-24c.

(69) Of course, it is noted that directly switching from the first to the third configuration can be commanded by the control unit of the pipette, by adapting the amplitude of the first downward stroke accordingly.

(70) FIGS. 14a to 14d and FIGS. 15a and 15B depict an operation aiming at switching from the third configuration to the second configuration of the module 50. For this, a second overstroke is commanded by the control unit, upwardly from the top pipetting position as shown in FIG. 14a.

(71) In this state of sampling the nominal volume associated with the third configuration, the body 66 is abutting up against the fixed body 22. As the second overstroke is continued upwardly, the top part 56a of the rotary member 56 is rotated because the follower rollers 68 press on their ramps 70b, as is depicted in FIG. 15a. This helical motion is transmitted to the bottom part 56b, as well as to its attachment fingers 64. It is made against the return strain generated by the second centring spring 80b, by compressing the latter. During this motion during which both pistons 24b, 24c slide while remaining rotatably fixed, the fingers 64 in helical motion progressively leave the slot 84c. At the end of the second overstroke, the fingers 64 are completely outside the slot 84c, such that the third piston 24c is uncoupled from the module 50. This state is shown in FIGS. 14b and 15b.

(72) Then, the control unit of the pipette commands a downward movement of the control rod 12, such that the fingers 64 repel the third piston 24c in its bottom position, abutting against the fixed body 22. This phase is represented in FIG. 14c. It precedes the final lifting back phase of the module 50 and of both pistons 24a, 24b, by virtue of an upward axial movement of the control rod 12 as depicted in FIG. 14d.

(73) Then, pipetting operations can be commanded conventionally, for volumes corresponding to the range associated with all of the two pistons 24a, 24b.

(74) FIGS. 16a and 16b as well as FIGS. 17a and 17b depict an operation aiming at switching from the second configuration to the first configuration of the module 50. For this, another second overstroke with a larger amplitude than the previous one is commanded by the control unit, upwardly from the top pipetting position as shown in FIG. 16a.

(75) In this state of sampling the nominal volume associated with the second configuration, the body 66 is abutting up against the fixed body 22. As the second overstroke is continued upwardly, the top part 56a of the rotary member 56 is rotated because the follower rollers 68 press on theirs ramps 70b, as is depicted in FIG. 16a. This helical motion is transmitted to the bottom part 56b, as well as to its attachment fingers 64. During this motion during which the piston 24b slides while remaining rotatably fixed, the fingers 64 in helical motion progressively leave the slots 84b. At the end of the second overstroke, the fingers 64 are completely outside the slots 84b, such that the second piston 24b is uncoupled from the module 50. This state is shown in FIGS. 16b and 17b.

(76) Then, the control unit of the pipette commands the downward movement of the control rod 12, such that the fingers 64 repel the second piston 24b in its bottom position, abutting against the fixed body 22 or against the third piston 24c already in a down abutting position. This phase, similar to that represented in FIG. 14c, precedes the final lifting back phase of the module 50 and of the single piston 24a, by virtue of an upward axial movement of the control rod 12.

(77) Then, pipetting operations can be commanded conventionally, for volumes corresponding to the range associated with the single first piston 24a.

(78) Once again, it is noted that directly switching from the third to the first configuration can be commanded by the control unit of the pipette, by adapting the amplitude of the second upward stroke accordingly.

(79) Of course, various modifications can be provided by those skilled in the art to the invention just described, only by way of non-limiting examples.