Pipette calibration and volume offset mechanism
A pipette calibration and volume offset mechanism. The calibration and volume offset mechanism is provided to facilitate user selectable calibration or volume offset operations of a pipette to which the calibration and volume offset mechanism is installed, through axial displacement of a threaded element that effectively moves the home position of the pipette. An offset counter of the calibration and volume offset mechanism is rotationally coupled to the threaded element during a volume offset operation to indicate offset magnitude, but decoupled from threaded element during a calibration or recalibration operation.
1. A pipette calibration and volume offset mechanism, comprising:
a housing;
a mode selection mechanism having a mode selector element movable between a first and second position, the mode selection mechanism being axially and rotationally constrained at a proximal end of the housing;
an axially displaceable follower element interposed between the mode selection mechanism and the housing and coupled to the mode selection mechanism;
an offset counter located within the housing and axially movable with the follower element;
a threaded element located within the housing and having an axial position that is adjustable to define a home position of a pipette when the calibration and volume offset mechanism is installed in the pipette;
a coupling located within the housing, the coupling rotationally coupled to the threaded element and operative to selectively rotationally couple the offset counter to or decouple the offset counter from the threaded element; and
a user rotatable input mechanism that is rotationally coupled to the coupling;
wherein, the offset counter will not rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the first position; and
wherein, the offset counter will rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the second position.
2. The pipette calibration and volume offset mechanism of claim 1 , wherein:
a mounting plate is coupled to the proximal end of the housing; and
the mode selection mechanism is interposed between the mounting plate and the housing.
3. The pipette calibration and volume offset mechanism of claim 1 , wherein the mode selection mechanism and the follower element are both barrel cams.
4. The pipette calibration and volume offset mechanism of claim 3 , wherein the mode selection barrel cam is at least partially nested within the follower barrel cam.
5. The pipette calibration and volume offset mechanism of claim 4 , wherein the coupling of the follower element to the mode selection mechanism comprises:
at least one arcuate or sloped cam slot on an outside surface of the mode selection barrel cam; and
at least one cam follower pin extending inward from the follower barrel cam and engaging the at least one cam slot in the mode selection barrel cam;
such that rotation of the mode selector barrel cam will produce an axial displacement of the follower barrel cam.
6. The pipette calibration and volume offset mechanism of claim 1 , wherein the offset counter is rotationally coupled to the coupling by a mechanism selected from the group consisting of the engagement of gear teeth or splines, and the engagement of corresponding tapers.
7. The pipette calibration and volume offset mechanism of claim 1 , wherein the user rotatable input mechanism is a pinion gear.
8. The pipette calibration and volume offset mechanism of claim 7 , wherein the coupling is provided with a miter gear that engages with the pinion gear to translate user rotation of the pinion gear into rotation of the coupling.
9. The pipette calibration and volume offset mechanism of claim 1 , further comprising a viewport in the housing for observing numerals or other indicators located on the offset counter.
10. The pipette calibration and volume offset mechanism of claim 1 , further comprising a user input mechanism access opening in the housing for allowing engagement and rotation of the user input mechanism.
11. The pipette calibration and volume offset mechanism of claim 1 , wherein upward axial movement of the offset counter is prohibited if the offset counter is in an offset position.
12. The pipette calibration and volume offset mechanism of claim 1 , wherein:
the threaded element and the housing are in threaded engagement; and
rotation of the input mechanism will result in rotation of the threaded element and axial displacement of the threaded element relative to the housing.
13. The pipette calibration and volume offset mechanism of claim 12 , wherein:
the threaded element forms a housing of a blowout assembly;
the blowout assembly further includes a blowout piston located in the blowout assembly housing; and
a blowout spring is located in the blowout assembly housing, distally of the blowout piston, such that the blowout piston is biased toward a proximal end of the housing.