Xerox 6250N Service Manual - Page 48
Color Registration Control, Light Density Setting, Light Density Adjustment
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UPC - 095205770407
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depending on the Transfer Roller surface condition or dirty condition of CTD (ADC) sensor surface. The light density emitted from the LED is controlled so that the reflected light density meets the specified value. This control is implemented in two ways: ■ Sets the light density so that the light reflected satisfies a specific value. ■ Adjusts the subsequent light density to be within a specific tolerance value. 1. Light Density Setting The reflected light density can vary greatly if the transfer roller has been replaced or the CTD (ADC) sensor has been cleaned. To deal with this variance the light density is reset when the power is turned on or the front cover is opened and closed. The intensity of the LED increases gradually and the set value is adjusted when the output of the CTD (ADC) sensor does not meet the specified value. If the output of the CTD (ADC) sensor does not reach the specified value, even though the light density is increased to the maximum limit, the controller signals the sensor is dirty. If the sensor output is extremely high, the controller will signal that the sensor is faulty. 2. Light Density Adjustment At the execution of automatic density control, the light density adjustment is made just before the patches for toner density control are generated. Light is emitted from the LED using the current light density setting, to check if the output value of the CTD (ADC) sensor is within the specified range. If the output value is low, light density is increased. If the output value is high, the light density is decreased. If the output value is less than the first lower limit, the controller signals the sensor as dirty and generates a warning. If the output value is less than the second lower limit, the controler signals that the sensor is faulty and stops the printing. Color Registration Control The printer uses a quad system where drums and developers are used exclusively for each of the four colors (yellow, magenta, cyan, and black). Images are formed on the drums, in the respective colors, and then layered to form one image. To avoid a positional shift between the different color images, the color registration control calculates how much the registration has shifted by comparing each of the other color patches in the registration string to the black bar that precedes it. Shift is corrected by adjusting the laser write timing to compensate. Color registration control is made depending on the internal temperature and print count at the execution of process control. Theory of Operation 2-9
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