Pipette mechanism

摘要

A dashpot piston mounted in a closed chamber is coupled by an axially movable shaft to a pipette piston to regulate return movement of the pipette piston within a pipette cylinder to draw fluid into the cylinder. The dashpot shaft is movable within limits relative to the dashpot piston to accommodate a blow-out of residual fluid from the pipette by the shaft driving the pipette piston beyond a home position to blow residual fluid from the pipette cylinder. An air inlet port in the bottom of the chamber allows air to be drawn into the chamber with upward movement of the dashpot piston while a valve adjacent to the air inlet port opens in response to downward movement of the dashpot piston to exit air from the chamber. Control of the relative sizes of the air inlet port and valve outlet regulates the relative rates of upward and downward piston movement in the cylinder. The dashpot piston carries a movable plate of a variable capacitor transducer for monitoring the position of the pipette piston within the pipette cylinder.