Image forming apparatus and method for performing image forming using an electrophotographic process

1. An image forming apparatus using an electrophotographic process comprising:

an image forming unit configured to perform monochrome printing and color printing;

a storage unit that stores print ratio data relating to printing in the image forming unit measured over time; and

a control unit configured to separately perform correction of monochrome toner density and correction of color toner density based on a predetermined first condition, if the first condition in the monochrome printing is met, the control unit performs correction of the monochrome toner density if a predetermined second condition relating to an amount of variation in the print ratio identified from the print ratio data is met.

2. The image forming apparatus using an electrophotographic process according to claim 1 comprising:

a first count unit that counts the number of prints or a printing time in the monochrome printing by integration;

a second count unit that counts the number of prints or a printing time in the color printing by integration; and

if the count value counted by the first count unit reaches a first density correction execution value, which is the first condition, the control unit performs correction of the monochrome toner density if the amount of variation in the print ratio in the monochrome printing is not less than a predetermined first threshold value, which is the second condition, and performs correction of the monochrome toner density and the color toner density if the count value counted by the second count unit reaches a second density correction execution value, which is the first condition.

3. The image forming apparatus using an electrophotographic process according to claim 2 ,

wherein, if the count value counted by the first count unit reaches the first density correction execution value, the control unit performs correction of the monochrome toner density and the color toner density if the amount of variation in the print ratio in the monochrome printing is not less than the first threshold value and the count value counted by the second count unit is not less than a predetermined second threshold value less than the second density correction execution value.

4. The image forming apparatus using an electrophotographic process according to claim 2 ,

wherein the control unit performs correction of the monochrome toner density if the count value counted by the first count unit reaches a predetermined third threshold value greater than the first density correction execution value.

5. The image forming apparatus using an electrophotographic process according to claim 1 ,

wherein the amount of variation in the print ratio is calculated based on an average print ratio from the second previous density correction to the previous density correction and an average print ratio from the previous density correction to the time when the first condition concerning the monochrome printing is met.

6. The image forming apparatus using an electrophotographic process according to claim 1 ,

wherein the storage unit is designed to store condition setting data and if the condition setting data has a certain value, the control unit performs correction of the monochrome toner density regardless of the second condition if the first condition concerning the monochrome printing is met.

7. The image forming apparatus using an electrophotographic process according to claim 1 ,

wherein the amount of variation in the print ratio is calculated as a difference between average print ratios.

8. The image forming apparatus using an electrophotographic process according to claim 1 ,

wherein the amount of variation in the print ratio is calculated as a ratio between average print ratios.

9. A method for performing image forming using an electrophotographic process comprising:

performing monochrome printing and color printing;

storing print ratio data relating to printing, measured over time; and

separately performing correction of monochrome toner density and color toner density based on the use of a predetermined first condition, if the first condition in the monochrome printing is met and if a predetermined second condition concerning an amount of variation in the print ratio identified from the print ratio data is met, correction of the monochrome toner density is performed.

10. The method according to claim 9 , comprising:

counting the number of prints or a printing time in the monochrome printing by integration;

counting the number of prints or a printing time in the color printing by integration; and

if the count value in the monochrome printing reaches a first density correction execution value, which is the first condition, correction of the monochrome toner density is performed if the amount of variation in the print ratio in the monochrome printing is not less than a predetermined first threshold value, which is the second condition, and performs correction of the monochrome toner density and the color toner density if the count value in the color printing reaches a second density correction execution value, which is the first condition.

11. The method according to claim 10 ,

wherein, if the count value in the monochrome printing reaches the first density correction execution value, correction of the monochrome toner density and the color toner density is performed if the amount of variation in the print ratio in the monochrome printing is not less than the first threshold value and the count value in the color printing is not less than a predetermined second threshold value less than the second density correction execution value.

12. The method according to claim 10 ,

wherein the correction of the monochrome toner density is performed if the count value in the monochrome printing reaches a predetermined third threshold value more than the first density correction execution value.