Developing apparatus

Claim 2

A developing apparatus comprising: a developer carrier (11) for carrying developer thereon and provided spaced opposite an electrostatic latent image holder (6) to form and maintain a very small gap between said carrier (11) and said holder (6); and voltage applying means (50) for applying an A.C. voltage, having a frequency which varies with time, across said gap between the carrier (11) and holder (6); whereby said developer is selectively caused to fly under the influence of an alternating electric field established by said A.C. voltage and to become attached to the holder (6).

Claim 3

A developing apparatus according to claim 1, characterized in that said A.C. voltage from said voltage applying means (50) has a period in which a plurality of different frequencies sequentially appear.

Claim 4

A developing apparatus according to claim 2, characterized in that said A.C. voltage is set so that said period occurs at least once during a time in which an electrostatic latent image on said holder (6) passes through an effective developing region in an area between said developer carrier (11) and said holder (6).

Claim 5

A developing apparatus according to claim 1, characterized in that said voltage applying means (50) comprises a transformer (51) having primary and secondary sides, a D.C. power source (52) connected to the primary side of said transformer, a switching circuit (55) for passing,and stopping a current from said D.C. power source (52) to said transformer (51), and switching control means for outputting to said switching circuit (55) a switching control signal whose frequency varies with time to turn ON and OFF said switching circuit (55), said transformer (51) generating said A.C. voltage whose frequency varies with time at the secondary side of the transformer (51).

Claim 6

A developing apparatus according to claim 4, characterized in that said switching control means comprises an oscillator (53) for outputting an oscillator signal having a predetermined frequency, and a programmable frequency divider (54) for switchingly frequency-dividing said oscillator signal (53) at a plurality of different frequency division ratios to output said switching control signal whose frequency varies with time, and in that the frequency of said switching control signal varies cyclically in a predetermined order of a plurality of different frequencies.

Claim 7

A developing apparatus according to claim 4, characterized in that said switching control means comprises a plurality of oscillators (56), (57) and (58) for outputting signals having a plurality of different frequencies, respectively, and switching means (59) for sequentially switching the output signals of said plurality of oscillators to output said switching control signal whose frequency varies with time, and wherein the frequency of said switching control signal varies cyclically in a predetermined order of a plurality of different frequencies.

Claim 8

A developing apparatus according to claim 2 or claim 3, characterized in that said plurality of different frequencies of said A.C. voltage from said voltage applying means (50) are set according to the characteristics of said developer.

Claim 9

A developing apparatus according to claim 8, characterized in that the width of said gap between said developer carrier (11) and said electrostatic latent image holder (6) is wider than the thickness of a toner layer on said developer carrier.

Claim 10

A developing apparatus comprising: a rotatable cylindrical developing roller (11) for carrying toner thereon and provided spaced opposite a rotatable photosensitive drum (6) for carrying an electrostatic latent image to define a very small gap between said roller (11) and said drum (6); means for supplying toner to a surface of said roller (11); a blade (12) for forming the toner on the roller to a layer having a predetermined thickness; and an A.C. bias power supply (50) electrically connected to said roller (11) for applying an A.C. voltage whose frequency varies with time to said gap between said drum (6) and roller (11), whereby said varying portions of the toner carried on the roller (11) are successively caused to fly to an electrostatic latent image formed on said drum (6) under the influence of an alternating electric field established by said A.C. voltage.

Claim 11

A developing apparatus comprising: a rotatable cylindrical developing roller (11) for carrying toner thereon and provided spaced opposite a rotatable photosensitive drum (6) for carrying an electrostatic latent image to define a very small gap between said roller (11) and said drum (6); means for supplying toner to a surface of said roller (11); a blade (12) for forming the toner on the roller to a layer having a predetermined thickness; and an A.C. bias power supply (50) electrically connected to said roller (11) for applying an A.C. voltage whose frequency varies with time to said gap between said drum (6) and roller (11), whereby said varying portions of the toner carried on the roller (11) are successively caused to fly to an electrostatic latent image formed on said drum (6) under the influence of an alternating electric field established by said A.C. voltage.

Claim 12

A developing apparatus as set forth in claim 9, characterized in that said A.C. voltage from said A.C. bias power supply (50) has a period in which a plurality of different frequencies sequentially appear stepwise, and said A.C. voltage is set so that said period occurs at least once during a time in which said electrostatic latent image passes through an effective developing region in said gap between said roller and said drum.