Variable volume positive displacement dispensing system and method

A method of dispensing viscous material onto a substrate using a dispensing system having a dispensing pump, the dispensing pump having at least three dispensing chambers each having a piston movable within the dispensing chamber to draw the viscous material into the dispensing chamber and to dispense the viscous material from the dispensing chamber, an inlet to receive material, an outlet from which material is dispensed, and a valve controllable between a first open position and a first closed position, such that in the first open position, the valve operatively couples the inlet to the one of the dispensing chambers to enable material to flow from the inlet to the one of the dispensing chambers, and in the first closed position the valve prevents material flow from the inlet to the one of the dispensing chambers, the method comprising steps of:

• loading the substrate into the dispensing system;
• positioning the dispensing pump over the substrate;
• moving one of the pistons in one of the dispensing chambers in a first direction for a first predetermined movement time to a retracted position to draw viscous material into the one of the dispensing chambers;
• maintaining the one of the pistons at the retracted position for a first predetermined dwell time;
• and
• moving the valve from the first open position to the first closed position at a first predetermined switch time after the one of the pistons has reached the retracted position and during the first predetermined dwell time,
• wherein the valve is controllable between a second open position and a second closed position such that in the second open position, the valve operatively couples the one of the dispensing chambers to the outlet to enable material to flow from the one of the dispensing chambers to the outlet, and in the second closed position the valve prevents material flow from the one of the dispensing chambers to the outlet, the method farther comprising the steps of:
• moving the one of the pistons in a second direction, opposite the first direction, for a second predetermined movement time to an extended position to dispense the viscous material from the one of the dispensing chambers;
• maintaining the one of the pistons at the extended position for a se pond predetermined dwell time;
• and
• moving the valve from the second open position to the second closed position at a second predetermined switch time after the one of the pistons has reached the extended position and during the second predetermined dwell time.