Optical writing device and image forming apparatus

An optical writing device comprising:

• a plurality of light-emitting points;
• a lens for transmitting light emitted from the light emitting points to focus the light on an object;
• a plurality of drive units for supplying drive currents to the plurality of light-emitting points respectively;
• a photodetector for outputting signals indicating quantities of light entering thereto from the respective light-emitting points;
• a gain switch unit for outputting photodetection signals obtained by amplifying the signals output from the photodetector in regard to the respective light-emitting points with gains preset for the respective light-emitting points;
• and
• a control unit for controlling the drive units such that the photodetection signals output from the gain switch unit in regard to the respective light-emitting points coincide with a value substantially equal to a predetermined reference value,
• wherein the gains for the respective light-emitting points are preset based on the transmittances of light emitted from the respective light-emitting points through the lens.

An optical writing device comprising:

• a plurality of light-emitting points;
• a lens for transmitting light emitted from the light emitting points to focus the light on an object;
• a plurality of drive units for supplying drive currents to the plurality of light-emitting points respectively;
• a photodetector for outputting signals indicating quantities of light entering thereto from the respective light-emitting points;
• a gain switch unit for outputting photodetection signals obtained by amplifying the signals output from the photodetector in regard to the respective light-emitting points with gains preset for the respective light-emitting points;
• and
• a control unit for controlling the drive units such that the photodetection signals output from the gain switch unit in regard to the respective light-emitting points coincide with a value substantially equal to a predetermined reference value,
• wherein the gains for the respective light-emitting points are preset based on the distances between the photodetector and the respective light-emitting points and the transmittances of light emitted from the respective light-emitting points through the lens.

An optical writing device comprising:

• a plurality of light-emitting points;
• a plurality of drive units for supplying drive currents to the plurality of light-emitting points respectively;
• a photodetector for outputting signals indicating quantities of light entering thereto from the respective light-emitting points;
• a gain switch unit for outputting photodetection signals obtained by amplifying the signals output from the photodetector in regard to the respective light-emitting points with gains preset for the respective light-emitting points;
• and
• a control unit for controlling the drive units such that the photodetection signals output from the gain switch unit in regard to the respective light-emitting points coincide with a value substantinally equal to a predetermined reference value,
• wherein the control unit is configured to receive photodetection signals from the gain switch unit while making the respective light-emitting points emit light under a predetermined initial condition and sets the gains for the respective light-emitting points preliminarily in the gain switch unit based on the received photodetection signals.