Patent ID: 7215896

Claim:
An image forming apparatus comprising an image retainer, a charger, an exposure unit, a plurality of developers, toner quantity indicators, an optical reflection density sensor, and a controller that operates to control image forming conditions by controlling the image retainer, the charger, the exposure unit, and the developers under a preset reference image forming condition to form a reference test-pattern toner image for controlling the image forming condition on the image retainer, by detecting a quantity of toner attached to the resulting reference test-pattern toner image from the output of the optical reflection density sensor, and by using a result of detection for control of a succeeding image forming condition, the controller being configured to form a test-pattern toner image for calibration of reflection density detection characteristics made by superimposing a plurality of toner images of different colors on the image retainer by the developers aside from the reference test-pattern toner image for controlling image forming conditions, to detect the quantity of toner attached to the test-pattern toner image for calibration of reflection density detection characteristics by the optical reflection density sensor, to calculate the detection characteristics of the optical reflection density sensor from the result of detection, and to calibrate the detection output characteristics of the optical reflection density sensor by the result of detection, wherein said controller controls said developer to form the test pattern toner image for calibration of the detection characteristics of the optical reflection density sensor by superimposing the plurality of toner images on the image retainer based on a detection signal from said toner quantity indicator and calibrates the detection output characteristics of the optical reflection density sensor by using the test pattern toner image for the detection characteristics of the optical reflection density sensor.