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Reciprocating antirotation pump

Reciprocating antirotation pump description/claims

This application is based on provisional application Ser. No. 60/876,413, filed Dec. 21, 2006.

This invention relates to a reciprocating pump capable of dispensing discrete microliter or milliliter liquid reagents. More particularly, this invention relates to such a pump which converts rotational motion to linear motion while utilizing an antirotational device.

The science and economics of invitro diagnostic (IVD) testing has changed with developments in assay reagent variation and assay size miniaturization. The number of assays performed annually is increasing as population demographics change and the availability of diagnostic testing increases throughout the world. Instrumentation is constantly adapted to these changing conditions. The reagents are harsher, including increased usage of salt solutions and acid and alkaline solutions having significant pH ranges. The liquid that pumps must move is decreasing from milliliters in volume to microliters in volume while precision and accuracy requirements remain constant. Lastly, the instrumentation is required to perform more tests prior to regular or unscheduled maintenance.

Pumps are used to move fluids within IVD instrumentation and to transfer reagents from a source reservoir to one or more test sites. As the assay volume decreases, more precise pumps are required. However, more precise pumps are more expensive to manufacture. Presently, there is an acute need for a precise and accurate pump that is also economical.

Piston pumps have been used in fluid dispensing applications for many years and four principle areas have consistently contributed to manufactured cost. They are the motor, the piston, the seal, and the anti-rotation mechanism. In addition, presently available pumps having a home position for the pump piston to provide a base value for the computer processing unit (CPU) which controls piston movement. Pumps are available with the piston home position being either in the piston aspirated position or in the piston retracted position. Accordingly, it would be desirable to simplify the anti-rotation mechanism by designing each part to be multi-functional and manufacturable with multiple processes including machined and injection molded methods. The manufacturing process flexibility helps to control costs during the initial time period prior to high volume production. In addition, it would be desirable to provide the pump user with a choice for the piston home position to provide flexibility in choosing a desired CPU.

The present invention provides a pump for liquids which utilizes a rotary motor capable of rotating clockwise and counterclockwise, a reciprocation pump piston and means for converting rotary motion to reciprocating linear motion. A lead screw which mates within a nut portion of a ferrule is rotated by the motor. The nut portion of the ferrule moves linearly and drives a piston portion of the pump to deliver discrete volumes of liquid. An antirotational construction is provided which prevents rotation of the nut portion of the ferrule. The dispense resolution of a pump, commonly stated as microliters per step, is proportional to the pitch of the lead screw. Since most piston pumps are built with off the shelf linear actuators, lead screw pitch is limited to those offered by the linear actuator manufacturer. This invention incorporates a standard stepper motor with a custom machined lead screw that is pressed onto the shaft enabling an infinite range of dispense resolutions.

The antirotation construction comprises a set of rails that fit into tracks. Either the rails or tracks can be positioned on the nut portion of the ferrule and the mating rails or tracks are positioned on a stationary housing for the nut portion of the ferrule. The length of the rails and tracks permits the pump piston to reciprocate between a fully aspirated position and a fully retracted position.

Variations in pump construction allow for additional features. The nut in the ferrule can be slotted and combined with a single or multiple o-rings as springs to provide low-cost mechanical anti-backlash compensation. In addition, the stepper motor which turns the lead screw can be made with a shaft protruding on both sides to provide two pump heads that are controlled simultaneously with one motor.

FIG. 1 is an exterior isometric view of the pump of this invention.

FIG. 2 is an exploded isometric view of the components of the pump of FIG. 1.

FIG. 3 is a side cross sectional view of the pump of this invention.

FIG. 4 is a cross section view through the rail and track of the ferrule of this invention.

FIG. 5 is an isometric view of the anti-backlash nut mechanism.

FIG. 6 is an isometric view of a two headed pump on one stepper motor.

• Provisional Patent
• Utility Patent

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