Image density correction method and image forming apparatus using the same

An image density correction method in an image forming apparatus provided with an image density adjustment capability, comprising:

• a patch image forming step of forming a plurality of toner amount detection patch images on an image supporter for each variation in a plurality of preset mutually different developing biases;
• a patch image density obtaining step of obtaining each density of the plurality of the formed patch images;
• an actual toner amount calculating step of obtaining each actual toner amount based on the obtained each density of the plurality of the patch images;
• a relational characteristics storing step of storing relational characteristics in which the actual toner amount is associated with each variation in the developing biases;
• and
• a developing bias setting step of setting a developing bias for realizing a preset reference toner amount based on the relational characteristics stored at the relational characteristics storing step and the reference toner amount, wherein
• the patch image forming step comprises a step of forming a between-sheet patch image at the set developing bias in a region on the image supporter between a plurality of sheets of paper during continuous printing,
• the patch image density obtaining step comprises a step of obtaining a density of the formed between-sheet patch image,
• the actual toner amount calculating step comprises a step of obtaining an actual toner amount based on the obtained density of the between-sheet patch image, and
• the developing bias setting step comprises a step of conducting an image density correction by determining whether the obtained actual toner amount is in agreement with the reference toner amount, reconstructing the relational characteristics stored at the relational characteristics storing step, by considering that both amounts to be made in agreement, when both amounts are determined as in disagreement, as a result of the determination, and resetting the developing bias for realizing the reference toner amount, based on the reconstructed relational characteristics and the reference toner amount.