Image forming apparatus and method of controlling development electric field strength therein

An image forming apparatus, comprising:

• an image carrier to carry an image on a surface thereof and rotate in a given direction;
• a latent image writing device to optically write an electrostatic latent image on the surface of the image carrier by changing a surface electric potential of the image carrier;
• a developing unit including a developer carrier disposed facing the image carrier in a development area of the image forming apparatus, the developer carrier carrying developer consisting essentially of toner and carrier on a surface thereof and rotating in a given direction, the developing unit attracting the toner adhering to the surface of the developer carrier to the electrostatic latent image formed on the surface of the image carrier to develop the electrostatic latent image in a development electric field formed between the electrostatic latent image on the surface of the image carrier and the surface of the developer carrier into a visible toner image that is then transferred onto a recording medium;
• a runout measurement information storage unit to store runout measurement information of the image carrier and runout measurement information of the developer carrier,
• the runout measurement information of the image carrier including runout amounts on the circumference of the image carrier in the development area and associating runout amount data obtained by measuring multiple runout measurement points located on the surface of the image carrier in a direction of movement of the surface of the image carrier with runout measurement point data indicating each of the multiple runout measurement points,
• the runout measurement information of the developer carrier including runout amounts on the circumference of the developer carrier in the development area and associating runout amount data obtained by measuring multiple runout measurement points located on the surface of the developer carrier in a direction of movement of the surface of the developer carrier with runout measurement point data indicating each of the multiple runout measurement points;
• a development gap measurement information storage unit to store development gap measurement information obtained by measuring a development gap at a time when a runout measurement point indicated in at least one of the runout measurement point data of the runout measurement information of the image carrier and a runout measurement point indicated in at least one of the runout measurement point data of the runout measurement information of the developer carrier come to face each other;
• and
• a development electric field strength control unit to obtain development electric field strength each time the runout measurement point indicated by the multiple runout measurement point data of the runout measurement information of the image carrier and the runout measurement point indicated by the multiple runout measurement point data of the runout measurement information of the developer carrier come to face each other in the development area, based on the runout measurement information of the image carrier and the runout measurement information of the developer carrier stored in the runout measurement information storage unit and the development gap measurement information stored in the development gap measurement information storage unit,
• the development electric field strength control unit determining development electric field strength control contents to cause all obtained development electric field strengths to fall within an acceptable target range for the development electric field strengths, and performing development electric field strength control according to the control contents.