Image forming apparatus with improved toner density control

An image forming apparatus, comprising:

• an image carrier;
• means for developing a latent image formed on the image carrier by applying two-component developer, including toner, onto the latent image, the developing means including a developing part containing the two-component developer and means for stirring the two-component developer;
• means for supplying toner to the developing part of the developing means;
• means for detecting a toner density of the two-component developer in the developing means;
• means for calculating a difference between an output value VT of the toner density detecting means and a criterion value VTref for controlling the toner density of the two-component developer and controlling the toner supplying means based upon the difference;
• means for detecting an image density of a criterion image formed on the image carrier;
• and
• means for correcting the criterion value VTref based upon an output value of the criterion image density detecting means,
• wherein the stirring means is operated and the criterion value VTref is corrected based upon determining a difference between the criterion value VTref and the output value VT of the toner density detecting means and an output value of the criterion image density detecting means when an image forming operation is started.

An image forming apparatus, comprising:

• an image carrier;
• a developing device configured to develop a latent image formed on the image carrier by applying two-component developer, including toner, onto the latent image, the developing device including a developing part containing the two-component developer and a developer stirring device configured to stir the two-component developer;
• a toner supplying device configured to supply toner to the developing part of the developing device;
• a toner density detection device configured to detect a toner density of the two-component developer in the developing device;
• a toner control device configured to calculate a difference between an output value VT of the toner density detect device and a criterion value VTref for controlling the toner density of the two-component developer and to control the toner supplying device based upon the difference;
• an image density detection device configured to detect an image density of a criterion image formed on the image carrier;
• and
• a criterion value correcting device to correct the criterion value VTref based upon an output value of the criterion image density detection device,
• wherein the developer stirring device is operated based upon determining a difference between the criterion value VTref and the output value VT of the toner density detection device and an output value of the criterion image density detection device when an image forming operation is started.

An image forming apparatus, comprising:

• an image carrier;
• a developing device configured to develop a latent image formed on the image carrier by applying two-component developer, including toner, onto the latent image, the developing device including a developing part containing the two-component developer and a developer stirring device configured to stir the two-component developer;
• a toner supplying device configured to supply toner to the developing part of the developing device;
• a toner density detection device configured to detect a toner density of the two-component developer in the developing device;
• a toner control device configured to calculate a difference between an output value VT of the toner density detection device and a criterion value VTref for controlling the toner density of the two-component developer and to control the toner supplying device based upon a result of the difference;
• an image density detection device configured to detect an image density of a criterion image formed on the image carrier;
• and
• a criterion value correcting device configured to correct the criterion value VTref based upon an output value of the criterion image density detection device,
• wherein the developer stirring device is operated and the criterion value VTref is corrected based upon determining a difference between the criterion value VTref and the output value VT of the toner density detection device and an output value of the criterion image density detection device when an image forming operation is started.

A method of controlling toner density of developer in a developing device of an image forming apparatus, comprising the steps of:

• detecting the toner density of the developer;
• controlling a toner supplying device supplying toner to the developing device based upon a difference between the detected toner density and a criterion value for the toner density;
• detecting an image density of a criterion image formed on an image carrier of the apparatus;
• and
• stirring the developer based upon determining the difference between the detected toner density and the criterion value for the toner density and the detected image density of the criterion image.