Patent ID: 8781348

Claim:
A transfer device comprising: an image carrier movable in a predetermined moving direction to carry a toner image; a first rotary body to contact an outer surface of the image carrier; a second rotary body pressed against an inner surface of the image carrier to form a transfer nip between the outer surface of the image carrier and the first rotary body; a transfer bias supply operatively connected to one of the first and second rotary bodies to supply a transfer bias, including a superimposed bias that includes a direct current component and an alternating current component superimposed on the direct current component for application to the image carrier, to transfer the toner image from the image carrier onto a recording medium conveyed through the transfer nip, wherein the direct current component of the transfer bias is provided to cause the other of the first and second rotary bodies to have an electrical potential higher than that of the image carrier and with a polarity opposite to a charge polarity of toner of the toner image, and wherein the alternating current component of the transfer bias has a returning peak with a polarity opposite to the polarity of the direct current component; and a controller operatively connected to the transfer bias supply to control the transfer bias supply, wherein the controller is configured to identify a recording medium type and to change a maximum value of the returning peak on the basis of the identified recording medium type, wherein the transfer bias supply increases the returning peak value in accordance with an increase in surface roughness of the recording medium corresponding to the identified recording medium type.