| 摘要 |
PURPOSE:To obtain stable printing density by detecting the denseness of a toner mark on a paper and controlling toner concentration in accordance with the denseness of the toner mark at the time of printing in color. CONSTITUTION:The latent image of the toner mark which is formed on a photosensitive drum 9 is developed with color toner in a 1st developing device 10 and with black toner, etc., in a 2nd developing device 11 and transferred to the paper 19. The transferred toner marks 16 and 17 are read by a reflection type optical sensor 4 and converted into digital data. A control part 7 discriminates the color which is developed at present and switches a correction part 20 which corrects the sensitivity difference of the sensor 4 to compare the numerical data of the denseness of the toner mark appropriate for the color with the numerical data of the denseness of the read-in toner marks 16 and 17 which is corrected. Based on the compared result, the proper quantity of toner is replenished to the 1st and the 2nd developing devices 10 and 11. Thus, the stable printing density is maintained in the case of using the black toner and color toner as well. |
