Electrophotographic apparatus that prevents toner from attaching to a contact member of a transfer device

An electrophotographic apparatus including charging means arranged at a predetermined charging position along a surface of a photosensitive member and developing means arranged at a predetermined developing position along the surface of the photosensitive member, the developing means including toner carrier means contacting the photosensitive member and carrier rotating means for rotating the toner carrier means, toner being charged to have a predetermined polarity by rotation of the toner carrier means, the photosensitive member having a predetermined point located at the developing position when the photosensitive member starts rotating, the apparatus comprising:

• first power supply means for generating a voltage having an opposite polarity to the predetermined polarity;
• a contact member arranged at a predetermined transfer position for applying the voltage generated by said first power supply means to a printing sheet disposed at said photosensitive member;
• second power supply means for generating a voltage having the predetermined polarity;
• switching means having at least a first state, in which the voltage generated by said first power supply means is applied to said contact member, and a second state, in which the voltage generated by said second power supply means is applied to said contact member;
• and
• control means for setting said switching means to the second state upon start of rotation of the photosensitive member and maintaining the switching means in the second state until said predetermined point on said photosensitive member passes the transfer position.

An electrophotographic apparatus comprising:

• developing means, arranged at a predetermined developing position, for forming a toner image on a photosensitive member;
• transfer means, arranged at a predetermined transfer position, for transferring, to a printing sheet, the toner image formed on said photosensitive member;
• aligning means for adjusting a posture of the printing sheet to be conveyed to the transfer position to a predetermined state, said aligning means being arranged at a predetermined position such that a distance of a convey path of the printing sheet from said aligning means to the transfer position is longer than a distance of a moving track of a surface of said photosensitive member from the developing position to the transfer position;
• and
• means for driving both the aligning means and the developing means.

An electrophotographic apparatus which is shifted from a normal mode to a predetermined standby mode if a printing instruction is not received for a predetermined period of time, the apparatus comprising:

• developing means, arranged at a predetermined developing position, for forming a toner image on a photosensitive member which is charged to have a predetermined polarity;
• transfer means for transferring the toner image formed on said photosensitive member to a printing sheet, the transfer means including
• a contact member arranged to contact a printing sheet arranged to contact said photosensitive member,
• first voltage generating means for generating a first voltage having an opposite polarity to the predetermined polarity,
• second voltage generating means for generating a predetermined second voltage having the predetermined polarity, and
• switching means having at least a first state, in which the first voltage is applied to said contact member, and a second state, in which the second voltage is applied to said contact member;
• and
• control means for setting said switching means to the first state when said apparatus is shifted from the standby mode to the normal mode, the control means further comprising means for maintaining the switching means in the first state while the apparatus is in the normal mode.

An electrophotographic apparatus having an openable/closable apparatus cover, the apparatus comprising:

• developing means for forming a toner image on a surface of a photosensitive member which is charged to have a predetermined polarity, the developing means including toner carrier means, carrier rotating means for rotating the toner carrier means, developing bias power supply means for generating a developing bias to be applied to said toner carrier means, and developing switching means for turning on/off application of the developing bias to said toner carrier means;
• transfer means for transferring the toner image formed on said surface of said photosensitive member to a printing sheet, the transfer means including a contact member arranged to contact a printing sheet arranged to contact said photosensitive member, first voltage generating means for generating a first voltage having an opposite polarity to the predetermined polarity, second voltage generating means for generating a second voltage having the predetermined polarity, and switching means having at least a first state, in which the first voltage is applied to said contact member, and a second state, in which the second voltage is applied to said contact member;
• detecting means for detecting that said apparatus cover is closed from an open state;
• and
• control means for setting, when said detecting means detects that said apparatus cover is closed from the open state, said switching means to the first and second states at least once in a state wherein said photosensitive member is charged, said developing switching means is turned on to apply the developing bias to said toner carrier means, and rotation of said toner carrier means by said carrier rotating means is stopped.

An electrophotographic apparatus comprising:

• developing means for forming a toner image on a photosensitive member, the developing means including a toner carrier roller made of an elastic member for carrying a toner to said photosensitive member, a developing blade contacting with the toner carrier roller for maintaining an amount of toner carried to said photosensitive member, and rotating means for rotating said toner carrier roller to charge the toner by friction with the developing blade;
• measuring means for measuring a period of time during which the rotation of said toner carrier roller is stopped;
• and
• control means for causing said rotating means to rotate said toner carrier roller by a predetermined amount before starting a printing operation when the period of time measured by the measuring means exceeds a predetermined length,
• wherein said developing means comprises a first motor for rotating said toner carrier roller and a second motor for rotating said photosensitive member.

An electrophotographic apparatus comprising:

• developing means for forming a toner image on a photosensitive member, the developing means including a toner carrier roller made of an elastic member for carrying a toner to said photosensitive member, a developing blade urged into contact with the toner carrier roller by a spring for maintaining an amount of toner carded to said photosensitive member, and rotating means for rotating said toner carrier roller to charge the toner by friction with the developing blade;
• measuring means for measuring a period of time during which the rotation of said toner carrier roller is stopped;
• and
• control means for causing said rotating means to rotate said toner carrier roller by a predetermined amount before starting a printing operation when the period of time measured by the measuring means exceeds a predetermined length.