Patent ID: 9042795
Filing Date: 2015-05-26
Classification: G03G

Abstract:
1. An image forming apparatus, comprising: an image carrier; a charging portion which charges the image carrier; an exposing portion which forms an electrostatic latent image on the image carrier charged by the charging portion; a developing portion which supplies toner to the electrostatic latent image for forming a toner image on the image carrier; a transfer member which forms a nip portion by cooperation with the image carrier, the nip portion being configured to nip a sheet on which the toner image is to be transferred; a discharging electrode member disposed to face the image carrier on a downstream side of the nip portion in a conveying direction of the sheet; a sheet conveying unit which conveys the sheet in such a manner that the sheet is passed through the nip portion and through a discharging gap, the discharging gap being formed by the discharging electrode member and the image carrier; a transfer bias voltage supplier which supplies, to the transfer member, a transfer bias voltage of a polarity opposite to a polarity of the toner for use in forming the toner image for transferring the toner image carried on the image carrier onto the sheet in the nip portion; and a separation bias voltage supplier which supplies, to the discharging electrode member, a separation bias voltage of a polarity opposite to the polarity of the transfer bias voltage for separating the sheet carrying the transferred toner image thereon from the image carrier, wherein the transfer bias voltage supplier is so configured that an absolute value of the transfer bias voltage to be supplied to the transfer member when a leading end and a trailing end of the sheet are passed through the nip portion is set smaller than an absolute value of the transfer bias voltage to be supplied to the transfer member when a transfer region of the toner image on the sheet is passed through the nip portion, the separation bias voltage supplier is so configured that an absolute value of the separation bias voltage to be supplied to the discharging electrode member when the leading end and the trailing end of the sheet are passed through the discharging gap is set smaller than an absolute value of the separation bias voltage to be supplied to the discharging electrode member when the transfer region is passed through the discharging gap, a first transfer bias voltage is the transfer bias voltage when the leading end and the trailing end are passed through the nip portion and a first separation bias voltage is the separation bias voltage when the leading end and the trailing end are passed through the discharge gap, and an absolute value of the first separation bias voltage to be supplied from the separation bias voltage supplier is increased as an absolute value of the first transfer bias voltage to be supplied from the transfer bias voltage supplier is increased, and the absolute value of the first separation bias voltage to be supplied from the separation bias voltage supplier is decreased as the absolute value of the first transfer bias voltage to be supplied from the transfer bias voltage supplier is decreased.