HP LaserJet Enterprise 500 Service Manual - Page 73
Image stabilization control
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If data from the color-misregistration and image-density sensors is outside a specified range when the product is turned on or when it is beginning the calibration sequence, the DC controller determines that these sensors have failed, and it notifies the formatter. Image stabilization control Environmental changes or deterioration of the photosensitive drums and toner can cause variations in the image density. The image-stabilization control reduces these fluctuations. There are three kinds of image stabilization controls. Table 1-13 Image-stabilization controls Image stabilization control Description Environment change control The environment change control calibrates each high-voltage bias to obtain an appropriate image according to the environment changes. The DC controller determines the environment where the product is installed based on the surrounding temperature and humidity data from the environment sensor, controls, and related biases. This control occurs under the following circumstances: ● The print cartridge is replaced. The DC controller notifies the formatter when it encounters a communication error with the environmental sensor. Image density control (DMAX) This control corrects variations in image density related to deterioration of the photosensitive drum or the toner. The DC controller adjusts the high-voltage biases to correct the problem under the following conditions: ● The sub thermistor detects a temperature that is too low when the product is turned on. ● After a specific period of the completion of a print operation ● A print cartridge is replaced. ● The ITB is replaced. ● A specified number of pages have printed. ● The formatter sends a command. ● The environment is relatively charged. Image halftone control (DHALF) The DC controller measures the halftone pattern according to the command from the formatter. The formatter performs this control to calibrate the halftone, based on the halftone-density measurements, under the following conditions: ● The formatter sends a command. ● DMAX is completed. The DC controller determines a RD sensor failure and notifies the formatter if it detects an out-ofspecified-data value from the RD sensor when the product is turned on or when the color misregistration control starts. ENWW Image formation system 37