JPS5497034A - Image quality controller for electrostatic copier - Google Patents

Abstract

PURPOSE:To form an excellent image of proper contrast, even a photosensitive element is deteriorated, by providing means for changing the toner density of a developing agent in accordance with the bias potential in addition to means for changing the bias potential in accordance with the surface potential of the photosensitive element. CONSTITUTION:When a photosensitive element 1 is deteriorated, the potential at a position corresponding to the white portion of an original is changed to as high as 250 V so that toners 15 are trapped even by the white portion. As a result, the texture of the copy obtainable by a transfer charger 4 is blotted. If, therefore, the bias voltage is increased, no trap of the toners takes place in the white portion. However, the attraction of the toners to the black portion is also weakened so that the image of the black portion is made thinner. In order to prevent this, there are provided both an amplifier circuit 13 for changing the reference voltage A of a toner density control circuit 10 in accordance with the output of a surface potential measuring circuit 6 and a circuit for a voltage dividing resistor 14 so that the concentration of the toners 15 is increased, when the deterioration in the photosensitive element is detected by the circuit 6, thus making it possible to obtain an excellent image of proper contrast.