Positive displacement pipetting system, having a design facilitating the gripping of the piston of the capillary-piston assembly

1. A pipetting system comprising:

a positive displacement sampling pipette; and

a capillary-piston assembly, a capillary of which is adapted to be fitted on a tip of the pipette, and a piston of which has a top end adapted to be held, during pipetting operations, by a gripping device equipping the pipette, said gripping device comprising a plurality of gripping tongs,

wherein, when the capillary of the capillary-piston assembly is fitted on the pipette tip and the gripping device is remote from the piston in an upward position, the gripping device can be displaced downwards with the plurality of gripping tongs in an open configuration, up to a determined position in which the gripping tongs, arranged around the top end of the piston, automatically switch into a closed configuration to hold the top end of the piston,

wherein said gripping device includes a tong lock in the open configuration, said tong lock including an unlocking control member slidably arranged between gripping tongs, and

wherein the pipette is constructed such that the automatic switching from the open configuration to the closed configuration is triggered by the displacement of the unlocking control member, caused by the top end of the piston bearing against said unlocking control member, during said downward displacement of the gripping device.

2. The system according to claim 1 , wherein said gripping device includes:

a head attached to the tongs;

an outside body arranged around the head and the gripping tongs, and including a sheath-shaped bottom end, enabling the gripping tongs to be opened/closed as a function of its relative position with respect to the gripping tongs which it surrounds, said tong lock in the open configuration.

3. The system according to claim 2 , wherein said tong lock comprises a locking system with balls.

4. The system according to claim 3 ,

wherein said tong lock comprises

locking balls accommodated in holes of said head of the gripping device, said holes radially opening into the outside;

a groove provided on an inside surface of said outside body;

first return elastic means forcing the tongs and the head upwards relative to said outside body; and

an axis system comprising at least a first portion and a second portion lower than the first portion, said first and second portions respectively having a first diameter as well as a second diameter smaller than the first diameter, and a lower end of said axis system being formed by said unlocking control member, and

wherein said tong lock is constructed such that

in the open configuration of the gripping tongs, the locking balls radially protrude outwards from said holes of the head, by being partially accommodated in said groove in which they are held by contact with said first portion of the axis system, said first return elastic means bringing said locking balls in abutment against a top axial end of said groove; and

when the second portion of the axis system is facing the locking balls, the combined actions of the first return elastic means and of the top axial end of the groove urge the locking balls to radially retract inwards into the holes of the head, until out of the groove and enabling said first return elastic means to cause an upward displacement of the gripping tongs and of the head relative to said outside body, up to a relative position bringing the gripping tongs into a closed configuration, surrounded by the sheath-forming bottom end of the outside body.

5. The system according to claim 4 , further comprising second return elastic means arranged between the outside body of the gripping device and a fixed element of the pipette.

6. The system according to claim 2 , wherein said pipette includes a control stem for displacing the head and the gripping tongs attached to the head.

7. The system according to claim 6 ,

wherein said control stem functions as an eject stem of the capillary-piston assembly, and

wherein the pipette further includes a pipetting control stem able to drive said gripping device into translation.

8. The system according to claim 6 , wherein said control stem functions as a pipetting control stem and an eject stem of the capillary-piston assembly.

9. The system according to claim 1 , wherein during an eject operation of the capillary-piston assembly, obtained by depressing an eject button and then releasing said eject button, the gripping tongs of said gripping device automatically switch from the closed configuration to the open configuration, and remaining in the open configuration at an end of said eject operation.