Pipette calibration and volume offset mechanism

A pipette calibration and volume offset mechanism, comprising:

• a calibration housing in the form of an internally threaded, substantially hollow cylinder;
• a mounting plate affixed to the proximal end of the housing;
• a barrel cam input having a mode selector element and interposed between the mounting plate and the calibration housing, the barrel cam input axially constrained by the calibration housing and the mounting plate;
• an axially displaceable barrel cam follower interposed between the barrel cam input and the calibration housing and coupled to the barrel cam input by a cam connection, the barrel cam follower rotationally constraining the barrel cam input, rotationally restrained by the calibration housing, and axially constrained by movement of the cam connection;
• a calibration counter located within the calibration housing, the calibration counter axially movable with the barrel cam follower but free to rotate relative thereto;
• a blowout assembly located within the calibration housing, the blowout assembly including:
• a housing having external threads that are in threaded engagement with the internal threads of the calibration housing, such that the blowout assembly housing is rotationally and axially constrained by the calibration housing,
• a blowout piston located in the blowout assembly housing, and
• a blowout spring located in the blowout assembly housing, distally of the blowout piston, such that the blowout piston is biased toward a proximal end of the calibration housing;
• a coupling located within the calibration housing between the calibration counter and the blowout assembly, the coupling axially restrained by the calibration housing but free to rotate therein, the coupling rotationally coupled to the blowout assembly and selectively rotationally coupleable to the calibration counter, so as to couple the calibration counter to or decouple the calibration counter from, the blowout assembly;
• and
• a user rotatable pinion gear that is rotationally coupled to the coupling and axially restrained by the calibration housing;
• wherein, rotation of the pinion gear will result in rotation of the blowout assembly housing and axial displacement of the blowout assembly relative to the calibration housing;
• wherein placement of the barrel cam input mode selector in a calibration position is operative, via the cam connection, to cause an upward axial movement of barrel cam follower and to thereby rotationally decouple the calibration counter from the coupling, such that the calibration counter will not rotate with the blowout assembly housing during rotation of the pinion gear;
• and
• wherein placement of the barrel cam input mode selector in an offset position is operative, via the cam connection, to cause a downward axial movement of barrel cam follower and to thereby rotationally couple the calibration counter to the coupling, such that the calibration counter will rotate with the blowout assembly housing during rotation of the pinion gear.