Patent ID: 8480323

Claim:
An expandable writing instrument for receiving a cartridge having a writing tip and a cartridge body, comprising: a writing end body section ( 10 ) having a barrel with a writing point including a bottom opening; a middle body section ( 30 ) fixed to the writing end body section; a rear body section ( 50 ) having a cap and liner in the cap, the rear body section being mounted to the middle body section for relative axial and non-rotational movement between an open position with the rear body section spaced away from the writing end body section, and a closed position with the rear body section being closer to the writing end body section; a spring in the writing point for engagement with the cartridge body of the cartridge in the writing instrument for biasing the cartridge upwardly; and a cam mechanism ( 70 ) operatively connected between the middle body section and the rear body section; the cam mechanism comprising: a helix cylinder ( 72 ) mounted to rotate and for axial movement in the liner, the liner having a peg ( 57 ) and the helix cylinder having a track ( 73 ) for slidably receiving the peg, the track being a closed loop extending entirely around the helix cylinder with a portion of right handed helix and a remainder of left handed helix, the track having offset upper and lower walls so that with axial movement of the rear body section toward and away for the writing end body section, the peg sliding in the track permits rotation of the helix cylinder continuously in one rotational direction, the helix cylinder having cam surfaces; and a shuttle ( 74 ) for receiving the cartridge body, mounted for axial movement in the helix cylinder with a shuttle cam ( 76 ) engaged to and movable with the shuttle, the shuttle cam being mounted for axial non-rotational movement to the middle body section and having shuttle cam surfaces that are slidably engaged against the cam surfaces of the helix cylinder, the cam surfaces of the helix cylinder having a high point that engages a flat portion of the shuttle cam surfaces for moving the shuttle, with rotation of the helix cylinder, to project the writing tip of a cartridge in the writing instrument, out of the bottom opening of the writing point when the rear body section is in the open position.