Image recording method including determining a gap between a photosensitive medium and a developing roller and apparatus therefor

An image recording method of forming a magnetic brush of a two-component developer on each of developing rollers provided in a plurality of developing units, respectively, forming a toner image of a first color on a recording area of photosensitive medium by a first one of said plural developing units and then forming a toner image of another color on the recording area of said photosensitive medium by a succeeding developing unit through contact of said magnetic brush with said photosensitive medium during a single rotation of said photosensitive medium, comprising the steps of:

• a) setting a waveform pattern of a current flowing between said photosensitive medium and a developing roller on the basis of a predetermined degree of contact of said magnetic brush with said photosensitive medium;
• b) applying a predetermined voltage between said photosensitive medium and the developing roller of at least one of said plural developing units;
• c) measuring a current flowing between said photosensitive medium and said developing roller upon application of said voltage;
• and
• d) selecting a gap between said photosensitive medium and said developing roller on the basis of magnitude of said current measured and a current waveform pattern representing degree of contact of said magnetic brush with said photosensitive medium while changing said degree of contact.

An image recording method of forming a magnetic brush of a two-component developer on each of developing rollers provided in a plurality of developing units, respectively, forming a toner image of a first color on a recording area of photosensitive medium by a first developing unit and then forming a toner image of another color on the recording area of said photosensitive medium by a succeeding developing unit through contact of said magnetic brush with said photosensitive medium during a single rotation of said photosensitive medium, comprising the steps of:

• a) setting a waveform pattern of a current flowing between said photosensitive medium and a developing roller on the basis of a predetermined degree of contact of said magnetic brush with said photosensitive medium;
• b) moving the developing roller of said developing unit away from said photosensitive medium to such an extent that said magnetic brush does not contact with said photosensitive medium;
• c) applying a predetermined voltage between said photosensitive medium and the developing roller of at least one of said plural developing units;
• and
• d) decreasing progressively a gap between said photosensitive medium and said developing roller in the state where said voltage is applied, monitoring magnitude of said current flowing between said photosensitive medium and said developing roller as well as said current waveform pattern, said current and said current waveform pattern changing as said gap decreases, and selecting the gap between said photosensitive medium and said developing roller so that a current waveform pattern as monitored coincides at least approximately with said predetermined waveform pattern.

An image recording method of forming a magnetic brush of a two-component developer on each of developing rollers provided in a plurality of developing units, respectively, forming a toner image of a first color on a recording area of photosensitive medium by a first developing unit and then forming a toner image of another color on the recording area of said photosensitive medium by a succeeding developing brush unit through contact of said magnetic brush with said photosensitive medium during a single rotation of said photosensitive medium, comprising the steps of:

• a) mounting a metallic drum having an electric resistance of substantially zero as said photosensitive medium;
• b) setting a waveform pattern of a current flowing between said metallic drum and a developing roller on the basis of a degree of contact of said magnetic brush with said metallic drum;
• c) applying a predetermined voltage between said metallic drum and the developing roller of at least one of said plural developing units;
• d) measuring a current flowing between said metallic drum and said developing roller upon application of said voltage;
• e) setting a gap between said metallic drum and said developing roller on the basis of magnitude of the current flowing between said metallic drum and said developing roller as well as said current waveform pattern representing the degree of contact of said magnetic brush with said metallic drum;
• and
• f) replacing said metallic drum by a semiconductive photosensitive medium after setting of said gap.

An image recording apparatus for forming a magnetic brush of a two-component developer on each of developing rollers provided in a plurality of developing units, respectively, forming a toner image of a first color on a recording area of photosensitive medium by a first developing unit and then forming a toner image of another color on the recording area of said photosensitive medium by a succeeding developing unit through contact of said magnetic brush with said photosensitive medium during a single rotation of said photosensitive medium, comprising:

• a) said photosensitive medium having a recording area on an outer surface thereof in which a toner image is formed in the course of rotation of said photosensitive medium;
• b) a power supply source for applying a predetermined voltage between said photosensitive medium and a developing roller of at least one of said plural developing units;
• c) a monitoring unit for measuring a current flowing between said photosensitive medium and said developing roller, converting the measured current into a pulse waveform and comparing said pulse waveform with a predetermined reference pulse waveform;
• d) a selecting unit for selectively determining a gap between said photosensitive medium and the developing roller of said at least one developing unit on the basis of result of the comparison available from output of said monitoring unit;
• and
• e) a moving unit for advancing or retracting said at least one developing unit toward or from said photosensitive medium on the basis of the gap determined by said selecting unit.