Patent ID: 7980197

Claim:
A dispenser for dispensing a volume of viscous material on a substrate, the dispenser comprising: a frame; a gantry system coupled to the frame; a viscous material supply coupled to the frame; a dispenser unit coupled to the gantry system, the dispenser unit comprising a housing having a chamber, a piston disposed in the chamber, a motor coupled to the piston to drive the movement of the piston within the chamber, a dispensing bore configured to receive the piston therein and in fluid communication with the viscous material supply, and a nozzle coupled to the housing, the nozzle having an orifice co-axial with the dispensing bore; and a controller coupled to the motor to control the operation of the motor, wherein the controller is configured to move the piston from a pre-dispense position in which viscous material is introduced into the dispensing bore to a dispense position in which the piston enters the dispensing bore to positively displace viscous material within the dispensing bore as the piston moves within the dispensing bore, and wherein the piston and the dispensing bore are configured such that a volume of viscous material dispensed from the dispensing bore is substantially equal to the volume of the piston entering the dispensing bore when moving the piston from the pre-dispense position to the dispense position, and wherein the orifice has a small-diameter bore in fluid communication with the dispensing bore, the small-diameter bore being smaller in diameter than the dispensing bore.