Dell 5110cn Color Laser Printer Service Manual - Page 568

Chapter 6 Principles of Operation 5.4.3 High Area Coverage Mode A continuous printing of the image of area coverage exceeding the toner dispense capability causes the toner density in the developer to be lowered. The High Area Coverage Mode extends the next page feed and dispenses the toner during this time, if the toner dispense time reached the specified value during a continuous printing. 5.4.4 Admix Mode Even the High Area Coverage Mode may not be able to cope with the reduction of toner density in the developer. Also, if the machine used in high humidity environment is relocated to the place in low humidity environment, the reference value of toner density is different in respective environments, thus causing large discrepancy between measured value by AUTOMATIC DENSITY CONTROL SENSOR and reference value of toner density. The Admix Mode dispenses the toner immediately to prevent the reduction of toner density, if the patch density result measured by the AUTOMATIC DENSITY CONTROL SENSOR is far lower than the reference value when the patches for toner density control are generated. 5.4.5 LED Light Quantity Control of AUTOMATIC DENSITY CONTROL SENSOR The AUTOMATIC DENSITY CONTROL SENSOR is a reflection type density sensor that radiates the light to an objective from the LED in the sensor and detects the reflected light from the objective to output electric signal according to the light quantity. For exact density measurement, the sensor output value (reflected light quantity) must be the specified value when no toner is put on the BTR as an objective. The reflected light quantity varies depending on the BTR surface condition or dirty condition of AUTOMATIC DENSITY CONTROL SENSOR surface. The light quantity emitted from the LED is controlled so that the reflected light quantity satisfies the specified value. This control is made in two ways; one to set the light quantity so that the reflected light quantity satisfies the specified value, and one to adjust the subsequent light quantity to be within the tolerance. 1) Light quantity setting The reflected light quantity may vary largely, if the Transfer Roller was replaced or the AUTOMATIC DENSITY CONTROL SENSOR was cleaned. Assuming this fact, the light quantity is set when the power is turned on, or the front cover is opened and closed. The light quantity of LED is increased gradually, and the set value is fixed when the output of AUTOMATIC DENSITY CONTROL SENSOR exceeds the specified value. At this time, if the output of AUTOMATIC DENSITY CONTROL SENSOR does not reach the specified value even though the light quantity is increased to the upper limit, the controller judges the sensor as dirty. Also, the controller judges the sensor as faulty in the event of extremely high output. 2) Light quantity adjustment At the execution of ADC, the light quantity adjustment is made immediately before the patches for toner density control are generated. The light is emitted from the LED with current setting of light quantity to check if the output value of the AUTOMATIC DENSITY CONTROL SENSOR is within the specified range. If the output value is low, the light quantity is increased by the specified amount at the next ADC, or if high, the light quantity is reduced at the next ADC. At this time, if the output value is less than the first lower limit, the controller judges the sensor as dirty and outputs the warning. Further, if less than the second lower limit, the controller judges the sensor as faulty and stops the printing. 6 - 49