Patent ID: 7690530

Claim:
A dispenser for viscous material packaged in a collapsible sleeve, said dispenser including a barrel having an elongate chamber for housing said viscous material packaged in said collapsible sleeve, said chamber including an opening at a distal dispensing end thereof, a closure removably retained on said distal end and having a peripheral surface partially overlying said opening and including a passage therein through which said viscous material can be dispensed as said sleeve is being collapsed, a piston rod within said elongate chamber and movable in the direction of elongation of said chamber, a piston connected to a forward end of said piston rod to move as a unit with said piston rod for engaging a portion of said collapsible sleeve as said viscous material is being dispensed by movement of said piston rod in a forward direction toward the distal dispensing end of said chamber, said piston including an outer peripheral edge closely adjacent an inner surface of said chamber, a movement limiting member connected to the piston rod and movable as a unit with said piston rod and piston, said movement limiting member including a distal surface extending forward of the piston a fixed distance from the outer peripheral edge of said piston and having a transverse dimension for engaging said peripheral surface of said closure to limit forward limiting movement of said piston rod and piston, said movement limiting member having an outer peripheral surface disposed inwardly of the inner surface of said chamber to provide an annular compartment defined by the piston, said outer peripheral surface of said movement limiting member and the inner surface of said chamber, portions of said collapsible sleeve being received in said annular compartment when the viscous material in said sleeve has been dispensed and the distal surface of the movement limiting member is in engagement with said peripheral surface of said closure, including a motor means for driving said piston rod and the piston and movement limiting member moveable with said piston rod in a forward dispensing direction until detection by said motor means of a predetermined force of engagement between the distal surface of said movement limiting member and the peripheral surface of said closure and thereafter discontinuing applying a driving force to said piston rod prior to a build up of an excessively high, potentially piston-damaging force between the piston and the viscous material being dispensed.