Patent ID: 7726516

Claim:
A minute quantity viscous material dispenser comprising a recipricatable material dispensing pumping piston aligned with a hollow dispensing tip, the piston having an end passing through a pre-dispense chamber containing a pressurized viscous material, a variable drive operably connected to the piston effect to drive the piston in opposite stroke directions towards and away from the tip, the piston effective to push material towards the tip as the piston moves towards the tip, a computer control controlling the drive, a piston position sensor operatively connected to the computer control and effective to output a signal reflecting the instantaneous position of the piston for at least a portion of the stroke of the piston by receipt at the sensor of energy outputted from a generally constant energy source, which energy output is variably blocked from the sensor by a linearly moveable blocking member connected to the piston and moveable in dependent response to movement of the piston, the blocking member positioned for movement between the source and the sensor and effective to block varying amounts of energy from the sensor while passing some amounts of energy to the sensor for at least a majority of the stroke of the piston, the sensor signal being reflective of the degree of blockage of the energy, the degree of blockage being directly proportional to the position of the blocking member with respect to the source and sensor, the computer control effective to control piston movement direction, piston movement pause, piston movement velocity and piston movement distance per pumping stroke.