Direct printing method with improved control function

A direct electrostatic printing method performed in consecutive print cycles, each of which includes at least one development period (t.sub.b) and at least one recovering period (t.sub.w) subsequent to each development period, said method comprising the steps of:

• providing a particle source, a back electrode and a printhead structure positioned therebetween, said printhead structure including an array of control electrodes;
• providing an image receiving medium between the array of control electrodes and the back electrode;
• producing a background electric field between the particle source and the back electrode to enable the transport of charged toner particles from the particle source toward the image receiving medium;
• during each development period (t.sub.b), applying variable electric potentials to the control electrodes to produce a pattern of electrostatic fields which, due to control in accordance with an image configuration, selectively permit or restrict the transport of charged particles from the particle source onto the image receiving medium;
• and
• connecting a supplemental voltage from at least one supplemental voltage source to generate a supplemental electric field between said particle source and said back electrode during a first portion of said development period, said supplemental electric field having a polarity selected to enhance the transport of charged particles from the particle source toward the image receiving medium, said supplemental electric field having a magnitude selected to be sufficient to increase transport of charged particles when transport is permitted by one of said control electrodes, said magnitude being insufficient to cause transport of charged particles from said particle source when transport is restricted by said one of said control electrodes.

A direct electrostatic print unit including:

• a particle source;
• a back electrode;
• a background voltage source connected to the back electrode to produce an electric potential difference between the back electrode and the particle source;
• a printhead structure positioned between the back electrode and the particle source, comprising:
• a substrate layer of electrically insulating material having a top surface facing the particle source and a bottom surface facing the back electrode;
• a plurality of apertures arranged through the substrate layer;
• a printed circuit arranged on said top surface of the substrate layer, including a plurality of control electrodes, each of which at least partially surrounds a corresponding aperture;
• a plurality of control voltage sources, each of which is connected to a corresponding control electrode to supply variable electric potentials to control a stream of charged toner particles through the corresponding aperture during each development period t.sub.b ;
• and
• at least one voltage source connected with reference to said control electrodes and said particle source to supply a periodic voltage pulse at the beginning of each development period t.sub.b to enhance the transport of toner particles from said particle source through the corresponding aperture at the beginning of each development period t.sub.b.

A direct electrostatic printing method performed in consecutive print cycles, each of which includes at least two development periods (t.sub.b) and at least one recovering period (t.sub.w) subsequent to each development period, the method comprising the steps of:

• producing a pattern of variable electrostatic fields during at least a part of each development period (t.sub.b) to selectively permit or restrict the transport of charged toner particles from a particle source toward a back electrode;
• producing a pattern of deflection fields to influence the trajectory of the transported charged toner particles;
• and
• producing an electric field during a first part of each development period (t.sub.b) to enhance the transport of toner particles from said particle source toward said back electrode.

A direct electrostatic printing method performed in consecutive print cycles, each of which includes at least two development periods (t.sub.b) and at least one recovering period (t.sub.w) subsequent to each development period, the method comprising the steps of:

• providing a particle source, a back electrode, and a printhead structure positioned therebetween, said printhead structure including an array of control electrodes and at least two sets of deflection electrodes;
• providing an image receiving medium between the array of control electrodes and the back electrode;
• producing an electric potential difference between the particle source and the back electrode to enable the transport of charged toner particles from the particle source toward the image receiving medium;
• during each development period (t.sub.b), applying variable electric potentials to the control electrodes to produce a pattern of electrostatic fields which, due to control in accordance with an image configuration, selectively permit or restrict the transport of charged toner particles from the particle source onto the image receiving medium;
• supplying a first variable deflection potential D1 to a first set of the at least two sets of deflection electrodes, and a second variable deflection potential D2 to a second set of the at least two sets of deflection electrodes;
• during at least one development period (t.sub.b), producing an electric potential difference between D1 and D2 to influence the symmetry of said electrostatic fields, thereby deflecting the transport trajectory of toner particles in a predetermined deflection direction;
• and
• connecting at least one voltage source to all control electrodes to supply a periodic voltage pulse which oscillates between a first potential level, applied during each development period (t.sub.b), and a second potential level (V.sub.kick) applied during a beginning of each development period to enhance the transport of toner particles from said particle source toward said back electrode.

A direct electrostatic printing method performed in consecutive print cycles, each of which includes at least one development period (t.sub.b) and at least one recovering period (t.sub.w) subsequent to each development period (t.sub.b), the method comprising the steps of:

• producing a pattern of variable electrostatic fields on a plurality of control electrodes proximate to apertures during at least a part of each development period (t.sub.b) to selectively permit or restrict the transport of charged toner particles from a particle source through said apertures toward a back electrode, said variable electrostatic field for one of said control electrodes having a first polarity to permit transport of toner particles through a respective one of said apertures and having a second polarity to restrict transport of toner particles through said respective one of said apertures;
• and
• producing a supplemental electric field on a plurality of guard electrodes during a first portion of each development period, said supplemental electric field having a polarity selected with respect to said charged toner particles to enhance the transport of toner particles from said particle source toward said back electrode, said supplemental electric field having an insufficient magnitude to cause transport of toner particles through said respective one of said apertures when said control electrode for said apertures has said electrostatic field selected to restrict transport of toner particles.

A direct electrostatic printing method performed in consecutive print cycles, each of which includes at least one development period (t.sub.b) and at least one recovering period (t.sub.w) subsequent to each development period, said method comprising the steps of:

• providing a particle source, a back electrode and a printhead structure positioned therebetween, said printhead structure including an array of control electrodes and guard electrodes;
• providing an image receiving medium between the array of control electrodes and the back electrode;
• producing a background electric field between a particle source and a back electrode to enable the transport of charged toner particles from the particle source toward the image receiving medium;
• during each development period (t.sub.b) applying variable electric potentials to the control electrodes to produce a pattern of electrostatic fields which, due to control in accordance with an image configuration, selectively permit or restrict the transport of charged particles from the particle source onto the image receiving medium;
• and
• connecting a supplemental voltage from at least one supplemental voltage source to the guard electrodes to generate a supplemental electric field between said particle source and said back electrode during a first portion of said development period, said supplemental electric field having a polarity selected to enhance the transport of charged particles from the particle source toward the image receiving medium, said supplemental electric field having a magnitude selected to be sufficient to increase transport of charged particles when transport is permitted by one of said control electrodes, said magnitude being insufficient to cause transport of charged particles from said particle source when transport is restricted by said one of said control electrodes.

A direct electrostatic printing method performed in consecutive print cycles, each of which includes at least two development periods (t.sub.b) and at least one recovering period (t.sub.w) subsequent to each development period, the method comprising the steps of:

• producing a pattern of variable electrostatic fields during at least a part of each development period (t.sub.b) to selectively permit or restrict the transport of charged toner particles from a particle source toward a back electrode;
• producing a pattern of deflection fields to influence the trajectory of the transported charged toner particles;
• and
• producing an electric field by a guard electrode during a first part of each development period (t.sub.b) to enhance the transport of toner particles from said particle source toward said back electrode.

A direct electrostatic print unit including:

• a particle source;
• a back electrode;
• a background voltage source connected to the back electrode to produce an electric potential difference between the back electrode and the particle source;
• a printhead structure positioned between the back electrode and the particle source, comprising:
• a substrate layer of electrically insulating material having a top surface facing the particle source and a bottom surface facing the back electrode;
• a plurality of apertures arranged through the substrate layer;
• a printed circuit arranged on said top surface of the substrate layer, including a plurality of control electrodes, each of which at least partially surrounds a corresponding aperture;
• a printed circuit arranged on said bottom surface of the substrate layer, including a plurality of guard electrodes, each of which at least partially surrounds a corresponding aperture;
• a plurality of control voltage sources, each of which is connected to a corresponding control electrode to supply variable electric potentials to control the stream of charged toner particles through the corresponding aperture during each development period t.sub.b ;
• and
• at least one voltage source connected to said guard electrodes to supply a periodic voltage pulse at the beginning of each development period t.sub.b to enhance the transport of toner particles from said particle source through the corresponding aperture at the beginning of each development period t.sub.b.