Pipetting unit with capacitive liquid detection, combination of such a pipetting unit and a pipetting tip, and method for capacitively detecting pipetting liquid
A pipetting unit ( 2 ) with capacitive liquid detection comprises: a pressure tube ( 10 ); a shield ( 12 ) disposed around the pressure tube ( 10 ); a coupling ( 14 ) for temporarily attaching a pipetting tip ( 4 ) to the pipetting unit ( 2 ), wherein when the pipetting tip ( 4 ) is connected, an electrical connection is established between the pressure tube ( 10 ) and the pipetting tip ( 4 ); and an electric circuit ( 20 ) coupled to the pressure tube ( 10 ) and the shield ( 12 ), wherein the electric circuit ( 20 ) is configured to apply a time-variable electrical signal to the pressure tube ( 10 ), said time-variable electrical signal permitting a capacitive detection of a contact between the pipetting tip ( 4 ) and a pipetting liquid ( 112 ) when the pipetting tip ( 4 ) is connected, and wherein the electric circuit ( 20 ) is configured to connect the shield ( 12 ) to ground.
1 . A pipetting unit configured for capacitive liquid detection, comprising:
a pressure tube;
a shield disposed around the pressure tube and movably supported relative to the pressure tube;
a coupling configured to temporarily attach a pipetting tip to the pipetting unit, wherein attachment of the pipetting tip to the coupling establishes an electrical connection between the pressure tube and the pipetting tip;
an ejection spring arranged at an end portion of the shield distal from the pipetting tip, wherein the shield is movable to exert an ejection force on the pipetting tip via the ejection spring; and
an electric circuit electrically coupled to the pressure tube and, via the ejection spring, to the shield,
wherein the electric circuit is configured to apply a time-variable electrical signal to the pressure tube, said time-variable electrical signal enabling capacitive detection of a contact between the pipetting tip and a pipetting liquid when the pipetting tip is attached, and wherein the electric circuit is configured to connect the shield to ground via the ejection spring.
2 . The pipetting unit according to claim 1 ,
wherein the time-variable electrical signal is a periodic signal.
3 . The pipetting unit according to claim 1 ,
wherein the electric circuit is configured to determine a resonant frequency of a portion of the pipetting unit and the pipetting tip that is excited when the time-variable electrical signal is applied.
4 . The pipetting unit according to claim 3 ,
wherein the electric circuit is configured to repeatedly or continuously apply the time-variable electrical signal to the pressure tube and to detect the contact between the pipetting tip and the pipetting liquid on the basis of a change in the resonant frequency.
5 . The pipetting unit according to claim 1 ,
wherein the electric circuit is configured to receive a time course of an electrical variable at the pressure tube and to detect a contact between the pipetting tip and the pipetting liquid from the time course of the electrical variable at the pressure tube.
6 . The pipetting unit according to claim 5 ,
wherein the electric circuit is configured to analyze the time course of the electrical variable with respect to at least one of amplitude, slope, integral, frequency, and phase, and based thereon, to detect a contact between the pipetting tip and the pipetting liquid.
7 . The pipetting unit according to claim 1 ,
wherein the electric circuit comprises at least one of the following features:
the electric circuit is implemented in the form of an integrated circuit component;
the electric circuit is implemented as a circuit with printed conductor paths;
the electric circuit is implemented as a flexprint, in particular as a multilayer flexprint.
8 . The pipetting unit according to claim 1 ,
wherein the electric circuit is fixed to the pipetting unit by means of a screw and wherein
the electric circuit is coupled to the pressure tube via the screw.
9 . The pipetting unit according to claim 8 ,
wherein the electric circuit is coupled to the pressure tube via the screw and a threaded hole or a screw nut.
10 . The pipetting unit according to claim 1 ,
wherein the ejection spring is at least arranged coaxially around the pressure tube or is made of steel.
11 . The pipetting unit according to claim 1 ,
further comprising an isolator arranged at an end portion of the shield facing the pipetting tip, wherein the isolator is arranged between the shield and at least one of the coupling and an attached pipetting tip.
12 . The pipetting unit according to claim 1 ,
wherein the shield is arranged coaxially with respect to the pressure tube.
13 . The pipetting unit according to claim 1 ,
wherein the coupling is an active coupling, in particular a solenoid-driven coupling, for fixing or releasing a pipetting tip.
14 . The pipetting unit according to claim 1 ,
further comprising a linear motor connected to the pressure tube, wherein a piston is movably arranged in the linear motor and wherein pressure changes in the pressure tube for aspirating or dispensing pipetting liquid are possible by movement of the piston.
15 . A pipetting system comprising a plurality of pipetting units, which are each designed according to claim 1 , wherein the pipetting system in particular comprises 96 pipetting units, which are each designed according to claim 1 .
16 . A combination of a pipetting unit and a pipetting tip, comprising:
a pipetting unit according to claim 1 ; and
a conductive pipetting tip attachable to the pipetting unit;
wherein the pipetting tip is a disposable pipetting tip and/or wherein the pipetting tip is made of a conductive polymer material.
17 . A method for capacitively detecting pipetting liquid by a pipetting unit, comprising:
applying a time-variable electrical signal to a pressure tube of the pipetting unit, from which the time-variable electrical signal is applied to a pipetting tip via a coupling;
providing a ground connection for a shield of the pipetting unit that is arranged around the pressure tube and that is movably supported relative to the pressure tube,
wherein the ground connection for the shield is provided via an ejection spring, which is arranged at an end portion of the shield distal from the pipetting tip, wherein the shield is movable to exert an ejection force on an attached pipetting tip via the ejection spring,
wherein the time-variable electrical signal and the ground connection are provided by a common electric circuit; and
detecting a contact between the pipetting tip and the pipetting liquid by means of the time-variable electrical signal.
18 . A computer program including program instructions which, when executed on a data processing system, effect a method according to claim 17 .