Method and apparatus for charging an electrographic photoreceptor

A charging device in which a surface of an image bearing device is charged in two steps before a latent image is formed on the image bearing device, comprising:

• a first contact charger for primarily charging the surface of the image bearing device in a state that the first contact charger receives a voltage that includes an AC component and a DC component superposed on the AC component;
• and
• a second contact charger for secondarily charging the surface of the image bearing device in a state that the second contact charger receives such a DC voltage as to discharge at least part of a pattern of charge potential variation of which a pitch corresponds to a frequency pitch of the AC component, caused in the primarily charging operation,
• wherein the DC voltage is applied to the second contact charger so as to entirely discharge a pattern of charge potential variation of which the pitch corresponds to the frequency pitch of the AC component, caused in the primary charging operation.

An image forming apparatus comprising:

• an image bearing device,
• first and second chargers, sequentially arranged for charging the image bearing device in a state that said first and said second chargers are in contact with said image bearing device,
• first voltage applying means for applying a voltage that includes an AC component and a DC component superposed on the AC component to said first charger, and second voltage applying means for applying to said second charger such a DC voltage as to discharge at least part of a pattern of charge potential variation of which a pitch corresponds to a frequency pitch of the AC component,
• wherein said second voltage applying means applies a DC voltage as to entirely discharge a pattern of charge potential variation of which the pitch corresponds to the frequency pitch of the AC component.

An image forming apparatus comprising:

• an image bearing device,
• a first contact charger which brings to contact with and charges onto a surface of said image bearing device,
• a second contact charger provided on a downstream side of said image bearing device with respect to said first contact charger,
• a first voltage applying means for applying said first contact charger with a voltage that includes an AC component and a DC component superposed on the AC component,
• a second voltage applying means for applying said second contact charger with a DC component, wherein
• the DC component applied to said second contact charger is determined, so that an absolute value of the peak voltage of the charging pattern by said first contact charger is larger than a discharging voltage by said second contact charger, when the charging of said image bearing device is deteriorated.