Image forming apparatus and method of controlling image forming apparatus

In an image forming apparatus comprising a developer supplying roller for supplying to a predetermined print position, a developer charged to a predetermined polarity, and a print head provided in the print position and having electrode pairs which are respectively provided with developer passing holes, each electrode pair comprising a first electrode and a second electrode connecting with each other and adapted such that said developer passing holes are opened and closed by control of an electric field generated between said first and second electrodes on the basis of print dot data sent in synchronization with a predetermined print clock signal, wherein

• said first electrode is grounded,
• power supplies, which differ in polarity and which are selectively connected to said developer supplying roller and ground by a selecting switch, are positioned between said developer supplying roller and ground,
• said selecting switch is so controlled that a power supply for generating said electric field such that said developer is attracted from said developer supplying roller to said first electrode between said developer supplying roller and said first electrode is selected from said power supplies at a time when the print dot data is sent in synchronism with said print clock signal, and
• said selecting switch is so controlled that a power supply for generating said electric field such that said developer is attracted from said first electrode to said developer supplying roller between said developer supplying roller and said first electrode is selected from said power supplies at a time when the print dot data is not sent in synchronism with said print clock signal.

In an image forming apparatus comprising:

• a developer supplying roller for supplying to a predetermined print position, a developer charged to a predetermined polarity;
• a print head provided in the print position and having electrode pairs which are respectively provided with developer passing holes, each electrode pair including a first electrode and a second electrode connecting with each other and adapted such that said developer passing holes are opened and closed by control of an electric field generated between said first and second electrodes on the basis of print dot data sent in synchronization with a predetermined print clock signal;
• first means for generating said electric field such that during printing said developer is attracted from said developer supplying roller to said first electrode between said developer supplying roller and said first electrode at a time when the print dot data is sent in synchronism with said print clock signal;
• second means for generating said electric field such that during printing said developer is attracted from said first electrode to said developer supplying roller between said developer supplying roller and said first electrode at a time when the print dot data is not sent in synchronism with said print clock signal;
• and
• means for applying ultrasonic vibration to said print head.

In an image forming apparatus comprising:

• a developer supplying roller for supplying to a predetermined print position, a developer charged to a predetermined polarity;
• a print head provided in the print position and having electrode pairs which are respectively provided with developer passing holes, each electrode pair comprising a first electrode and a second electrode connecting with each other and adapted such that said developer passing holes are opened and closed by control of an electric field generated between said first and second electrodes on the basis of print dot data sent in synchronization with a predetermined print clock signal;
• and
• means for applying ultrasonic vibration, wherein
• said first electrode is grounded,
• power supplies, which differ in polarity and which are selectively connected to said developer supplying roller and ground by a selecting switch, are positioned between said developer supplying roller and ground,
• said selecting switch is so controlled that a power supply for generating said electric field such that said developer is attracted from said developer supplying roller to said first electrode between said developer supplying roller and said first electrode is selected from said power supplies at a time when the print dot data is sent in synchronism with said print clock signal,
• said selecting switch is so controlled that a power supply for generating said electric field such that said developer is attracted from said first electrode to said developer supplying roller between said developer supplying roller and said first electrode is selected from said power supplies at a time when the print dot data is not sent in synchronism with said print clock signal, and
• said means for applying ultrasonic vibration applies ultrasonic vibration to said print head.

A method of controlling an image forming apparatus in which:

• a developer is charged to a predetermined polarity and is supplied to a predetermined print position by a developer supplying roller, a print head has electrode pairs which are respectively provided with developer passing holes, each electrode pair including a first electrode and a second electrode connecting with each other and provided in the print position, said developer passing holes being opened and closed by control of an electric field generated between said first and second electrodes on the basis of print dot data sent in synchronization with a predetermined print clock signal, and a means is provided for applying ultrasonic vibration, said method comprising the steps of:
• generating said electric field such that during printing said developer is attracted from said developer supplying roller to said first electrode, said electric field being generated between said developer supplying roller and said first electrode at a time when the print dot data is sent in synchronism with said print clock signal,
• generating said electric field such that during printing said developer is attracted from said first electrode to said developer supplying roller, said electric field being generated between said developer supplying roller and said first electrode at a time when the print dot data is not sent in synchronism with said print clock signal, and
• applying ultrasonic vibration to said print head by said means for applying ultrasonic vibration.