HP Color 9850mfp Service Manual - Page 144
IMAGE STABILIZATION CONTROL, 14.1 Toner density control, 14.2 Dmax control
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II UNIT EXPLANATION IMAGE STABILIZATION CONTROL 14. IMAGE STABILIZATION CONTROL hp Color 9850mfp 14.1 Toner density control The purpose of this control is to correct the reference value of toner density for each color against variable factors of the image density such as environmental factors. A. Explanation of the operation The charging amount of toner changes depending on the environmental factors such as the temperature and humidity. And in proportion to the length of time since developer was last used, toner tends to be hard to get charged. The reference value of toner density is varied to correct these changes in the charging amount of toner. B. Timing of the operation • When the environmental factors such as the temperature and/or humidity change. • For each elapsed hour of the use of developer 14.2 Dmax control The purpose of the Dmax control is to set the highest image density for each color to the reference level. The Dmax control is carried out by the gamma sensor (PS11), drum motors Y, M, C and K (M14, M15, M16 and M17), transfer belt motor (M18), 1st transfer pressure/release motor (M19) and the developing motors Y, M, C and K (M20, M21, M22 and M23), and controlled by the printer control board (PRCB). Related sensors include the temperature/humidity sensor (TEMP/HUM). A. Explanation of the operation With a patch image created on the transfer belt at the maximum exposure amount, each density is read by the gamma sensor (PS11). This operation is repeated several times while changing a developing bias value each time. The developing bias value obtained when the density reaches the reference level is stored as an optimum developing bias value of the engine and developing is made at this developing bias value. B. Timing of the operation • When the main switch (SW2) is turned on for the first time in 6 hours or more after it was turned off. • When the job starts 6 hours or more after the SW2 has been turned on. • Every 1,000 pages of output. However at the time of completion of the job, when the 1,000th page is contained in the job. • When the humidity has changed more than 30% RH from the value measured at the last operation. 2-70