Two colour electrostatic copier calibration technique

摘要

The technique uses a single surface potential sensor (12) between the first and second developer units, and a detector to capture the dark damping characteristic of the photosensitive body. The photosensitive body is illuminated with a test image of specific luminosity to form an image on the body. The surface potential sensor is used to monitor the test image. The control voltage is varied to a position at which the surface potential sensor is set, on the basis of the characteristic modification device output. The measured potential is compared with the control voltage, when modified by a step change to control the voltage or illumination of the test image so as to use the measured potential as a control voltage. A further test image is formed, and the second developer unit is calibrated in the same way.