Image forming apparatus

An image forming apparatus comprising:

• an image bearer;
• a transfer-bias power source to output a transfer bias including a direct current (DC) component and an alternating current (AC) component to transfer a toner image from the image bearer to a recording sheet;
• and
• a controller to control a printing speed and the transfer-bias power source to change the DC component and the AC component, according to the printing speed and a duty of the transfer bias,
• the duty being A/(A+B)×100[%]
• where
• A denotes an area on a return-directional side to move toner from the recording sheet back to the image bearer, relative to a center value (Voff) of a maximum value and a minimum value of the transfer bias in one cycle of a waveform of the transfer bias A=a return-directional time period t1×|Voff—a return-directional voltage peak value Vrdp|,
• B denotes an area on a transfer-directional side to move the toner from the image bearer to the recording sheet, relative to the center value (Voff) in the one cycle, B=a transfer-directional time period t2×|Voff—a transfer-directional voltage peak value Vtdp|.

An image forming apparatus comprising:

• an image bearer;
• a transfer-bias power source to output a transfer bias including a direct current (DC) component and an alternating current (AC) component;
• a transfer circuit to receive the transfer bias to transfer a toner image from the image bearer to a recording sheet;
• a detector to detect a resistance of the transfer circuit;
• and
• a controller to control the transfer-bias power source to change the AC component, according to the resistance of the transfer circuit detected by the detector and a duty of the transfer bias,
• the duty being A/(A+B)×100[%]
• where
• A denotes an area on a return-directional side to move toner from the recording sheet back to the image bearer, relative to a center value (Voff) of a maximum value and a minimum value of the transfer bias in one cycle of a waveform of the transfer bias A=a return-directional time period t1×|Voff—a return-directional voltage peak value Vrdp|,
• B denotes an area on a transfer-directional side to move the toner from the image bearer to the recording sheet, relative to the center value (Voff) in the one cycle, B=a transfer-directional time period t2×|Voff—a transfer-directional voltage peak value Vtdp|.