Electrophotographic image forming apparatus comprising means for automatically adjusting image reproduction density

An electrophotographic image forming apparatus comprising:

• a photoconductor;
• charger means for electrically charging said photoconductor to a predetermined initial electric potential;
• light projecting means for projecting a light onto said photoconductor electrically charged to the predetermined initial electric potential so as to form an electrostatic latent image on said photoconductor;
• developing means for developing the electrostatic latent image formed on said photoconductor with toner so as to form a toner image on said photoconductor;
• voltage applying means for applying a developing bias voltage to said developing means;
• and
• density control means for controlling said charger means and said voltage applying means to change the initial electric potential and the developing bias voltage, said density control means controlling said charger means and said voltage applying means so that a difference between the initial electric potential and the developing bias voltage becomes larger and a value of the following ratio becomes larger as the absolute value of the initial electric potential becomes larger:
• (V.sub.B `V.sub.Im)/(Vo-V.sub.Im),
• where V.sub.B is the developing bias voltage,
• Vo is the initial electric potential, and
• V.sub.Im is an electric potential on the surface of said photoconductor in the case of a maximum light amount of the light projected from said light projecting means onto said photoconductor.

An electrophotographic image forming apparatus comprising:

• a photoconductor;
• charger means for electrically charging said photoconductor to a predetermined initial electric potential;
• light projecting means for projecting a light onto said photoconductor electrically charged to the predetermined initial electric potential so as to form an electrostatic latent image on said photoconductor;
• developing means for developing the electrostatic latent image formed on said photoconductor with toner so as to form a toner image on said photoconductor;
• voltage applying means for applying a developing bias voltage to said developing means;
• detection means for detecting a state of said photoconductor;
• storage means for storing a plurality of gradation correction data for correcting a gradation of an image to be formed;
• selecting means for selecting one of the plurality of gradation correction data stored by said storage means based on the developing bias voltage and the initial electric potential;
• correcting means for correcting an image density signal for representing densities of respective pixels of the image to be formed based on the gradation correction data selected by said selecting means;
• light projecting control means for controlling a light amount of the light projected from said light projecting means onto said photoconductor according to the image density signal corrected by said correcting means;
• and
• density control means for controlling said charger means and said voltage applying means to change the initial electric potential and the developing bias voltage based on a detection result of said detection means, said density control means controlling said charger means and said voltage applying means so that a difference between the initial electric potential and the developing bias voltage becomes larger and a value of the following ratio becomes larger as the absolute value of the initial electric potential becomes larger:
• (V.sub.B -V.sub.Im)/(Vo-V.sub.Im),
• where V.sub.B is the developing bias voltage,
• Vo is the initial electric potential, and
• V.sub.Im is an electric potential on the surface of said photoconductor in the case of a maximum light amount of the light projected from said light projecting means onto said photoconductor.