Electronic pipettor with improved accuracy
A hand-held electronic pipettor is designed particularly to be programmed and operated with one hand for the convenience of the user. It uses a capacitance touchpad control for programming, and a separate run button for the operating mode. Internal components are located so that the center of gravity of the pipettor is located within the palm of the user. Flash memory stores an empirically derived table that correlates aspiration volume to motor steps and a separate empirically derived table the correlates dispensing volumes to motor steps.
1. In a hand-held electronic pipettor having an aspiration cylinder and piston, a stepper motor that drives the piston in the aspiration cylinder, a microprocessor, and a user interface display, a method of aspirating and dispensing liquid volumes comprising the steps of:
selecting an aspiration volume;
using an aspiration lookup table to determine a number of motor steps necessary to aspirate the selected aspiration volume, wherein values in the aspiration lookup table representing the number of motor steps necessary to aspirate respective volumes are determined empirically to account for aspiration inaccuracies in the pipettor;
instructing the motor to move the piston to a home position and then instructing the motor to retract the piston the determined number of motor steps in order to aspirate the selected aspiration volume into a disposable pipettor tip mounted to the pipettor;
selecting a dispensing volume;
using a dispensing lookup table to determine a number of motor steps necessary to dispense the selected volume, wherein the values of motor steps necessary to dispense respective volumes in the dispensing lookup table are determined empirically to account for dispensing inaccuracies;
instructing the motor to extend the piston the determined number of motor steps in order to dispense the selected dispense volume from the disposable pipettor tip mounted to the pipettor.
2. The invention as recited in claim 1 where the pipettor further comprises flash memory, and further wherein the aspiration lookup table and the dispensing lookup table both reside in flash memory, and the microprocessor instructs the motor to retract and extend.
3. The invention as recited in claim 2 wherein flash memory also includes a plurality of acceleration profiles corresponding to various levels of maximum pipetting speed.
4. The invention as recited in claim 1 wherein the hand-held electronic pipettor further comprises flash memory in which the aspiration lookup table resides, and further wherein:
the user selects an aspiration volume from choices displayed on the user interface display, a translator correlates each of the displayed aspiration volumes to an index value, and the aspiration lookup table correlates the index value for the displayed aspiration volume selected by the user to a corresponding retraction distance in terms of motor steps necessary to retract the piston in order to aspirate the selected aspiration volume.
5. The invention as recited in claim 1 wherein the hand-held electronic pipettor further comprises flash memory in which the dispensing table resides, and further wherein:
the user selects one or more dispensing volumes from choices displayed on the user interface display, a translator correlates each of the displayed dispensing volumes to an index value, and the dispensing lookup table correlates the index value for the displayed one or more dispensing volumes selected by the user to corresponding extension distances in terms of the motor steps necessary to extend the piston in order to dispense the selected one or more volumes.
6. The invention as recited in claim 2 wherein the aspiration lookup table and dispensing lookup table contain values empirically determined and pre-loaded onto the flash memory, and a user can calibrate the aspiration lookup table or the dispensing lookup table by programming the pipettor to shift the values in the respective tables.
7. The invention as recited in claim 2 wherein the aspiration lookup table and dispensing lookup table residing in flash memory can be replaced by an alternative aspiration lookup table or dispensing lookup table.
8. The invention as recited in claim 1 wherein the pipettor uses further comprises a battery and the microprocessor controls average electrical current from the battery to the stepper motor via pulse width modulation.
9. The invention as recited in claim 8 wherein the average electrical current from the battery to the stepper motor is limited at motor start up to reduce acceleration.