Image formation system and density controlling method

An image formation system comprising:

• a first image forming apparatus;
• a sheet inversion section;
• a second image forming apparatus;
• an image density detection section;
• and
• an inter-apparatus density adjusting section;
• the first image forming apparatus including:
• a first photoconductor;
• a first charging section configured to charge a surface of the first photoconductor;
• a first light exposure section configured to irradiate the first photoconductor with light to form an electrostatic latent image;
• a first development section configured to supply developer to visualize the electrostatic latent image;
• a first image bearing member configured to bear a visualized toner image that is to be transferred to a first surface of a sheet;
• a first fixing section configured to fix a toner image transferred to a sheet;
• a first toner image density detection section configured to detect a density of a toner pattern borne on the first image bearing member;
• and
• a first density control section configured to control an image formation condition such that a detection result of the first toner image density detection section matches a first target control density determined by a first density control point;
• the sheet inversion section being disposed on a downstream side of the first image forming apparatus in a sheet conveyance direction, and configured to invert a sheet output from the first image forming apparatus;
• the second image forming apparatus being disposed on a downstream side of the sheet inversion section in the sheet conveyance direction, and including:
• a second photoconductor;
• a second charging section configured to charge a surface of the second photoconductor;
• a second light exposure section configured to irradiate the second photoconductor with light to form an electrostatic latent image;
• a second development section configured to supply developer to visualize the electrostatic latent image;
• a second image bearing member configured to bear a visualized toner image that is to be transferred to a second surface of a sheet;
• a second fixing section configured to fix a toner image transferred to a sheet;
• a second toner image density detection section configured to detect a density of a toner pattern borne on the second image bearing member;
• and
• a second density control section configured to control an image formation condition such that a detection result of the second toner image density detection section matches a second target control density determined by a second density control point;
• the image density detection section being disposed on a downstream side of the second image forming apparatus in the sheet conveyance direction, and configured to detect a density of a first pattern image for a highest density adjustment and a density of a second pattern image for a half-tone density adjustment, each of the first and second pattern images being formed on a sheet in each of the first image forming apparatus and the second image forming apparatus;
• the inter-apparatus density adjusting section being configured to correct the first density control point or the second density control point on a basis of a detection result of the first pattern image of the image density detection section, and to correct a light exposure energy of the first light exposure section or a light exposure energy of the second light exposure section on a basis of a detection result of the second pattern image, wherein
• the first density control section corrects the first density control point or the light exposure energy of the first light exposure section in accordance with a coverage rate of an image formed in the first image forming apparatus, and
• the second density control section corrects the second density control point or the light exposure energy of the second light exposure section in accordance with a coverage rate of an image formed in the second image forming apparatus.