1. Technical Field
The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile machine, or a multi-function apparatus having one or more capabilities of the above devices, and in particular, to an image forming apparatus that can properly correct charging voltage to be applied to a charging member such as a charging roller.
2. Background Art
In an electrophotographic image forming apparatus, such as a copier and a printer, it is necessary to adjust the charging voltage to be applied to the charging member in order to reliably form a quality image even though performance of the image carrier, such as a photoconductor drum, or the charging member, such as a charging roller, has been degraded over time or due to environmental changes.
Several approaches have been tried. For example, the current/voltage when the rated voltage or current is applied to the charging roller is measured, and the resistance of the charging roller is obtained from the results. From a relation between the obtained resistance and the temperature detected by a temperature sensor, variation of the charged potential is forecasted and the charging voltage to be applied to the charging roller is corrected as needed. Alternatively, the temperature of the charging roller is detected and the charging voltage to be applied to the charging roller is corrected based on the detection results. Further alternatively, a surface potentiometer is used to detect the surface potential (charged potential or the exposure potential) of the photoconductor drum and image forming conditions, such as charging voltage to be applied to the charging member, are adjusted based on the surface potential of the photoconductor drum detected by the surface potentiometer.