Developing device and image forming apparatus and process cartridge incorporating same

An image forming apparatus comprising:

• a latent image bearer to bear a latent image thereon;
• a developing device to develop the latent image with developer including toner and magnetic carrier to form a toner image, the developing device including a developer bearer to carry, by rotation, developer including toner and magnetic carrier to a development range facing a latent image bearer, the developer bearer including:
• a magnetic field generator having multiple magnetic poles;
• and
• a cylindrical developing sleeve to rotate and bear developer on an outer circumferential face thereof with magnetic force of the magnetic field generator provided inside the developing sleeve,
• the developing sleeve including a base to maintain a cylindrical shape of the developing sleeve and a low friction surface layer including a material lower in friction coefficient with toner than a material of the base;
• a voltage application device to apply, to the developing sleeve, developing bias voltage including an AC component;
• and
• a duty ratio controller to control, according to an image area ratio of an image to be developed, a duty ratio of the AC component of a developing bias voltage,
• wherein when the image area ratio is 30% or smaller, in the AC component of the developing bias voltage, the duty ratio controller sets a duty ratio of an opposite polarity component, a polarity of which is opposite a toner normal charge polarity, to 3% or smaller.

An image forming apparatus comprising:

• a latent image bearer to bear a latent image thereon;
• a developing device to develop the latent image with developer including toner and magnetic carrier to form a toner image, the developing device including a developer bearer to carry, by rotation, developer including toner and magnetic carrier to a development range facing a latent image bearer, the developer bearer including:
• a magnetic field generator having multiple magnetic poles;
• and
• a cylindrical developing sleeve to rotate and bear developer on an outer circumferential face thereof with magnetic force of the magnetic field generator provided inside the developing sleeve;
• a voltage application device to apply, to the developing sleeve, developing bias voltage including an AC component;
• and
• a duty ratio controller to control, according to an image area ratio of an image to be developed, a duty ratio of the AC component of a developing bias voltage,
• wherein when the image area ratio is 30% or smaller, in the AC component of the developing bias voltage, the duty ratio controller sets a duty ratio of an opposite polarity component, a polarity of which is opposite a toner normal charge polarity, to 3% or smaller.