Patent ID: 8568141

Claim:
A linear cartridge-type motorized dental syringe, comprising: a housing in which a motorized syringe unit is fixedly incorporated, the motorized syringe unit comprising a casing provided with a coupling having, at a front end thereof, a cylindrical space in which a cartridge holder is inserted, the coupling functioning to detachably couple the inserted cartridge holder to the syringe unit, and a motor comprising a reduction gear, said geared motor being secured to a rear end of a fixed casing, an externally threaded plunger rod located in alignment with an axis of a drive shaft of the geared motor, the plunger rod being movable longitudinally of the casing but not rotatable relative to the casing, a rotating cylindrical body located coaxially in the casing and operatively connected to the drive shaft of the geared motor such that it can be rotated by the drive shaft, a nut including a pair of arm-like nut halves protrusive forward beyond a forward end of the rotating cylindrical body and having, on forward inner surfaces of the nut halves, internal threads adapted to engage external threads on the plunger rod, a locking ring located for rotation around a longitudinal axis of the plunger rod and for longitudinal movement between a rearward position wherein the locking ring forces the internal threads on the arm-like nut halves to engage the external threads on the plunger rod, and a forward position wherein the locking ring releases the mutual engagement of the internal and external threads, pusher pins adapted to be pushed by the cartridge holder for moving the locking ring from the forward position to the rearward position when the cartridge holder is inserted in and coupled to the cylindrical space, and a coil spring for pushing the locking ring back to the forward position when the cartridge holder is not in the cylindrical space, the rotation of the rotating cylinder body resulting in rotative motion of the nut around the plunger rod to linearly move forward the plunger rod.