Dell 5110cn Color Laser Printer Service Manual - Page 566

Chapter 6 Principles of Operation 5.4 Process Control For a stable printing, the parameters related to the image forming must be corrected as necessary. The control of entire printing process including parameter correction control is called "process control". Mainly, the following two controls are made: - Potential control - Toner density control To supplement these two controls, the following controls are provided: - High Area Coverage Mode - Admix Mode - AUTOMATIC DENSITY CONTROL SENSOR LED light quantity setting 5.4.1 Potential Control To attain stable printing image density, the drum charging voltage and the developing DC voltage are adjusted according to the developing capability of each color carrier that varies momentarily. The adjusted drum charging voltage and the developing DC voltage are fed back to keep the printing image density constant. The potential control is made immediately before the start of printing, if either of the following conditions is satisfied: - At the first printing after the power on - When cumulative print count after the power on exceeds 25 - When a cleaning cycle is executed during continuous printing The outline of control is as follows. 1) The AUTOMATIC DENSITY CONTROL SENSOR (temperature and humidity sensor) detects the temperature and humidity, and sets target values of drum charging voltage and developing DC voltage. 2) The patches of respective colors (yellow, magenta, cyan, and black) for the potential control are generated and transferred on the BTR. (For the shape of patches, see the following figure.) About 11mm Y About 12mm M About 3mm About 57mm C K engine principle0046FA 3) The AUTOMATIC DENSITY CONTROL SENSOR (density sensor) detects the density of the area on BTR where no toner is present and the density of patches. 4) The density measured in step 3) is compared with target value set in step 1) to change the drum charging voltage and the developing DC voltage for each color according to a difference. 6 - 47