Importance

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Abstract

A hand held self-contained automated pipette for portable operation having an electrically operated digital linear actuator. The actuator preferably includes a stepper motor driving a rotor. A threaded screw is coaxially positioned within the rotor and is connected to an actuator shaft having elongate grooves slidable in a guide for preventing shaft rotation so that precise linear motion is imparted to the shaft. A pipetting displacement assembly having one of various sizes is removably attached for actuation by a common actuator including programmed movement of a displacing piston in a displacement cylinder to optimize air interface volume, neutralize variations in vacuum pipette effects, and provide an accommodated stroke and readout for improved accuracy while pipetting and/or titrating different ranges of volumes. A control circuit is provided so that the back EMF of the stepper motor coils is recirculated when power is duty-cycled off for power conservation. Conversely, recirculation is switched off when power is duty-cycled on for minimizing losses. Recirculation is switched off when coils are commutated which produces a rapid magnetic field collapse for assuring high torque. Upon calibration the piston undertakes immediate excursion to an end of travel limit and after motor slippage is retracted to a home position. This home position is chosen for optimum preservation of an air interface volume between drawn liquid and the piston tailored with particularity to the displacement assembly being used. Multiple precision modes including pipetting, multiple dispensing, titration, and dilution, are provided. Other features are also disclosed.

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First Claim