| 摘要 |
PROBLEM TO BE SOLVED: To form an easily recognizable printed image by determining thickness of recording paper on the basis of its light transmitting quantity and reducing printing density when the recording paper is thin. SOLUTION: When a light quantity measuring sensor 22 is driven, light is emitted from a light emitting diode 22a so as to irradiate recording paper conveyed on a conveying path A, the light transmitted through the recording paper is received by means of an optical sensor 22b, and then, the light quantity data is fed to an A/D terminal in a MPU. In the MPU, the light quantity data is converted from analog data into digital data so as to be compared with the data stored in a table. If the light quantity data is smaller, it is decided that the recording paper is comparatively thick one, so that bias voltage control to a developing roll 9 from a high voltage unit 12 is not carried out similarly to the case of not being in a bias variable mode. On the other hand, if the light quantity data is larger, it is decided that the recording paper is thin one, so that an absolute value for the bias voltage to the developing roll 9 is lowered, and printing density is reduced. |
