Patent ID: 8029205

Claim:
A writing instrument for receiving an elongate cartridge having a writing tip at a first end thereof and an opposing second end, the writing instrument comprising: first and second retainers that are mutually connected to define a chamber having a longitudinal axis; at least one axially-extending rib disposed on the first retainer, the rib terminating in a tip; an axially-aligned aperture in the second retainer that is sized for withdrawing and inserting the cartridge therethrough; a plunger held in the chamber for axial sliding movement; a groove in the plunger, the groove receiving the rib for preventing rotation of the plunger; a plurality of plunger teeth on the plunger; a rotary ratchet held in the chamber for rotation about the longitudinal axis and sliding movement parallel to the longitudinal axis; a plurality of ratchet teeth on the ratchet, the ratchet teeth cooperating with and opposing the plunger teeth and rib tip so as to impel rotation of the ratchet about the longitudinal axis when a stem is pressed and released; a concavity between two of the ratchet teeth; a longitudinal channel in the ratchet; a compression spring disposed in the chamber, the compression spring urging the rotary ratchet toward the tip of the rib such that the tip is received in the concavity when the ratchet is in an extended position and the rib is received in the channel when the ratchet is in a retracted position, and prehensile means having a cavity complementary to the second end of the cartridge for grasping the cartridge such that the prehensile means and attached cartridge are moved longitudinally with the rotary ratchet between the extended and retracted positions.