Image forming apparatus and image density control method

An image forming apparatus, comprising

• a latent image carrier;
• a charge device configured to charge the latent image carrier with a prescribed potential;
• a latent image forming device configured to form a latent image on the surface of the latent image carrier;
• a developing device having a developer carrying member configured to carry developer at least including toner, said developing device applying a development bias to the developer carrying member and transferring the toner on the developer carrying member to the latent image on the latent image carrier and developing the latent image;
• a transfer device configured to transfer a toner image from the latent image carrying member to a transfer member;
• an optical detection device configured to detect a light reflected from the toner image on one of the latent image carrier and the transfer member;
• a control device configured to periodically form a gradation sequence pattern having at least two toner patches formed based on a different image formation condition attracting a different amount of toner from each other, said control device calculating a developing ability of the developing device based on a detection value detected by the optical detection device from the at least two toner patches, said control device adjusting the image formation condition based on the calculated developing ability;
• and
• a factor detection device configured to detect a contributing factor causing the developing ability to largely change after the last adjustment of the image formation condition;
• wherein said control device controls image formation such that when the factor detection device does not detect the contribution factor, the at least two toner patches are partially formed based on a prescribed fixed image formation condition so that a toner attraction amount attracting to the part of the at least two toner patches enters a prescribed range detectable for the optical detection device, while forming the remaining toner patches of the at least two toner patches based on a prescribed image formation condition determined in accordance with the image formation condition previously adjusted;
• and
• wherein when the detection device detects the contribution factor, the entire toner patches are formed based on the prescribed fixed condition.

A method for controlling density of an image, comprising the steps of:

• periodically forming a gradation sequence pattern including at least two toner patches using a different image formation condition attracting a different amount of toner with each other;
• detecting the at least two toner patches with an optical detection device;
• adjusting an image formation condition based on a detection value detected in the step of detecting the at least two toner patches;
• and
• forming at least one toner patch based on a prescribed fixed image formation condition so that an attraction amount of toner attracting to the at least one toner patch can enter a prescribed detectable range for a sensor within a variable range of development gamma defined by a relation between a toner attraction amount and a development potential, while forming the rest of the at least one toner patch in accordance with the image formation condition adjusted last time so that data of a toner attraction amount attracting to the rest of the at least one toner patch enter the prescribed range dispersing substantially at the same interval.