Fuji Xerox Co., Ltd.

Katsuhiko Nishizawa

Takayoshi Suzuki

Tsuneo Toda

Driving electric current values of a semiconductor laser when detected light amount values are equal to each of five light amount values having respectively different magnitudes are detected. Thus, five detecting points relating to a light amount value-driving electric current value characteristic are obtained. A differential efficiency .eta. at an interval between two adjacent detecting points is calculated. For example, a differential efficiency .eta.1 is calculated from an adjacent detecting point and a differential efficiency .eta.2 is calculated from another adjacent detecting point. Further, values of the differential efficiencies are displayed on a display so that an operator can recognize an exact deteriorated state of an LD from the values of the differential efficiencies.

Image forming device

Light scanning devices forming electrostatic latent images on photosensitive bodies are disposed so as to correspond respectively to the plurality of photosensitive bodies which correspond to a plurality of colors, respectively. Electrooptical elements are disposed on light paths of light beams. The electrostatic latent images formed on the respective photosensitive bodies 1 are respectively developed by developing means. Developed electrostatic latent images are respectively superposed together and transferred onto a sheet, so that a color image is formed. Images-for-detecting-offset-amounts, which are formed on a conveying body by the light scanning devices, are detected, and offset amounts of images of the respective colors are detected. Based on detected offset amounts, voltages are applied to the respective electrooptical elements such that the offset amounts become values of a predetermined range.

Color image forming apparatus having correction of color image offset

A digital image forming apparatus is constructed to accurately detect period abnormality of a horizontal sync signal. In the apparatus, a sync signal generation portion outputs the horizontal sync signal by a received light signal from a light position detector. A sync signal abnormality monitor monitors whether a detected period of the sync signal is longer than a reference period, or it is normal. When the output signal of the sync signal is judged to be longer than the reference period, an abnormality detecting signal is supplied to a continuous turning-on portion. When the continuous turning-on portion receives the abnormality detecting signal, it issues an instruction to a synchronizing turning-on portion so that video data continues to be turned on, that is, turning-on signal is continuously outputted. Since a laser beam is continuously turned on by this instruction, the light position detector can certainly receive the laser beam. Accordingly, the period of the sync signal can be accurately detected and the cause of period abnormality can be specified.

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Saitama, Japan

Katsuhiko Nishizawa