Patent ID: 7694857

Claim:
A material dispensing pump comprising: a feed screw including a cylindrical neck portion and a helical feed path defined between a major diameter and a minor diameter of the feed screw; a closed-loop servo-motor having indexed rotational positions that drives the feed screw during a dispensing operation; a dispensing controller that generates control signals to control the servo-motor, wherein the servo-motor performs the dispensing operation in response to the control signals; a feed screw housing having a cavity, the feed screw extending through the cavity, the feed screw housing having an inlet port and an outlet port in communication with the cavity, the helical feed path being substantially sealed from ambient air between the inlet port and the outlet port by an O-ring positioned about the neck between the neck and the feed screw housing and a threaded spanner nut that applies pressure in a direction along a longitudinal axis of the feed screw that compresses the O-ring about the neck to substantially seal the helical path from ambient air; a pressure unit for applying positive pressure to cause material to be presented to the inlet port at a desired rate during the dispensing operation such that the material flows through the helical feed path toward the outlet port; and a material suspension unit for placing the material in the substantially sealed helical feed path in suspension by applying negative pressure to the material following the dispensing operation.