Image forming apparatus having transfer bias control

An image forming apparatus, comprising:

• an image bearing member to bear a toner image on a surface thereof;
• a nip forming member to contact the surface of the image bearing member to form a transfer nip therebetween;
• a transfer bias output device to output a transfer bias to form a transfer electric field including an alternating electric field in the transfer nip to transfer the toner image from the image bearing member onto a recording medium interposed in the transfer nip, the transfer bias including a superimposed bias in which an alternating current (AC) bias is superimposed on a direct current (DC) bias;
• an information receiving device to receive information including at least one of temperature, humidity, a thickness of the recording medium delivered to the transfer nip, a surface condition of the recording medium including a depth of a recessed portion thereof, and an amount of toner adhered to the surface of the image bearing member per unit area;
• and
• a controller operatively connected to the information receiving device and the transfer bias output device, to cause the transfer bias output device to change a target output value of a peak-to-peak voltage of the AC bias based on the information obtained by the information receiving device and reduce an absolute value of a target output value of the DC bias as the target output value of the peak-to-peak voltage of the AC bias increases.