Patent ID: 8219009

Claim:
A method of electrographic printing in a printer having a photoconductor member, and a developer station including a magnetic roller having a radius R s having a rotating magnetic core having a center and surrounded by a toning shell tangent to the photoconductor member along a line, and a reservoir of developer formed from magnetic carrier particles having a magnetization of M (emu/g) and toner particles, wherein the radius of the magnetic roller (r) from the centerline of the magnetic core to a point on the magnetic roller is determined as follows: r = ( δ 2 + R S 2 - 2 ⁢ ⁢ δ ⁢ ⁢ R S ⁢ cos ⁡ ( θ - β ) ) 1 2 , where θ is an angular distance between the first nip and a second nip wherein the second nip is formed between the toning shell and a developer conveyor roller, R S is a radius of the toning shell, δ is an offset distance of the toning shell from the center of the magnetic core of radius R C , and β is an angular distance between a line of closest approach of the rotating magnetic core and the toning shell, and B 0 is the magnetic field at the surface of the magnetic core in the center of a north or south pole in Gauss and the second nip such that the following conditions are met, that is that a magnetic force F M for a magnetic core with N pole pairs on a carrier particle with magnetization M emu/g and mass m is directed toward the center of the magnetic core, and has magnitude in g's that is determined as follows: F M (in g's )=( MB 0 N ( R c )/g)*( R c /r) N *( R c /r 2 ) that is that F M <1 g's at some portion of the toning roller in a strip zone area of the toning shell where the developer is removed and returned to the sump and also satisfies the condition of F M >1 g's within 120° of the line, comprising the steps of: rotating the magnetic core relative to the toning shell during a printing operation such that magnetic carrier particles on the toning shell are subjected to at least about 190 pole flips per second, and delivering developer to the toning shell at an angular distance no more than about 120° from the tangent line between the toning shell and the photoconductor member to reduce a residence time that the developer stays on the developer shell prior to transfer of toner particles from the toning shell to the photoconductor element.