Image forming apparatus

An image forming apparatus configured to execute an image forming operation, the image forming apparatus comprising:

• a rotatable image bearing member on which an electrostatic latent image is formed;
• a developing unit including a developer container that accommodates a developer including a toner and a carrier, and a developer bearing member that bears the developer to develop the electrostatic latent image formed on the image bearing member into a toner image;
• a transfer member to which the toner image borne on the image bearing member is transferred;
• a carrier collecting device that includes a rotatable sleeve disposed to face the image bearing member and a magnet non-rotatably disposed inside the sleeve, and collects the carrier on the image bearing member,
• a bias application unit that applies a bias including an AC voltage to the sleeve;
• and
• a controller that controls the bias application unit, wherein
• the sleeve is disposed downstream of a development position at which the electrostatic latent image formed on the image bearing member is developed and upstream of a transfer position at which the toner image borne on the image bearing member is transferred to the transfer member, in a rotation direction of the image bearing member,
• the controller controls the bias application unit to apply a first bias to the sleeve during the image forming operation, and controls the bias application unit to apply a second bias to the sleeve in a predetermined mode during non-image forming, and
• when, in one period of the AC voltage of the bias applied to the sleeve by the bias application unit, a duration of a voltage of a reverse polarity to a charging polarity of the toner with respect to a DC potential of the sleeve is t1, a duration of a voltage of a same polarity as the charging polarity of the toner with respect to the DC potential of the sleeve is t2, and a ratio of t1 with respect to one period (t1+t2) of an AC voltage of the bias applied to the sleeve by the bias application unit is a duty ratio, a duty ratio of the AC voltage of the second bias is lower than 50%.

An image forming apparatus configured to execute an image forming operation, the image forming apparatus comprising:

• a rotatable image bearing member on which an electrostatic latent image is formed;
• a developing unit including a developer container that accommodates a developer including a toner and a carrier, and a developer bearing member that bears the developer to develop the electrostatic latent image formed on the image bearing member into a toner image;
• a transfer member to which the toner image borne on the image bearing member is transferred;
• a carrier collecting device that includes a rotatable sleeve disposed to face the image bearing member and a magnet non-rotatably disposed inside the sleeve, and collects the carrier on the image bearing member,
• a bias application unit that applies a bias in which a DC voltage and an AC voltage are superimposed to the sleeve;
• and
• a controller that controls the bias application unit, wherein
• the sleeve is disposed downstream of a development position at which the electrostatic latent image formed on the image bearing member is developed and upstream of a transfer position at which the toner image borne on the image bearing member is transferred to the transfer member, in a rotation direction of the image bearing member,
• the controller controls the bias application unit to apply a first bias to the sleeve during the image forming operation, and controls the bias application unit to alternately apply a second bias and a third bias to the sleeve in a predetermined mode during non-image forming,
• a polarity of the DC voltage of the first bias is the same as a charging polarity of the toner,
• the second bias is a bias that is superimposed with the DC voltage at which a polarity of a potential of the sleeve with respect to the image bearing member is negative and the AC voltage, and
• the third bias is a bias that is superimposed with the DC voltage at which the polarity of the potential of the sleeve with respect to the image bearing member is positive and the AC voltage.