Developer station and method for an electrographic printer with magnetically enabled developer removal

A developer station for an electrographic printer having a photoconductor drum, and a horizontally oriented image transport webbing tangent to said drum at one of a 12 o'clock position and a 6 o'clock position, comprising:

• a sump of magnetic developer comprising toner and carrier having a magnetization of M (emu/g), and a magnetic roller having a radius Rs mounted above said sump and including a rotatable magnetic core having a center surrounded by a substantially cylindrical toning shell rotatably mounted with respect to the core, said shell being adjacent to the photoconductor drum and defining a nip,
• wherein the distance (r) from the center 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 point on the toning shell (70) and the nip between the toning shell and the photoconductor drum, RS 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 RC, and β is an angular distance between a line of closest approach of the rotating magnetic core and the toning shell, and the nip such that the following conditions are met, that is that FM<1 g at some portion of the toning roller in the strip zone and also satisfies the condition of FM>1 g within 120° of the nip.

A method of electrographic printing in a printer having a photoconductor member, and a developer station including a magnetic roller having a radius Rs 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 center 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 developer delivery point on the toning shell (70) and the nip between the toning shell and the photoconductor drum, RS 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 RC, and β is an angular distance between a line of closest approach of the rotating magnetic core and the toning shell, and the nip such that the following conditions are met, that is that FM<1 g at some portion of the toning roller in the strip zone and also satisfies the condition of FM>1 g 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.