HP Color 9850mfp Service Manual - Page 147

II UNIT EXPLANATION hp Color 9850mfp 14.5 Gamma correction control IMAGE STABILIZATION CONTROL The gamma correction control detects the gamma characteristics of the image density against the exposure amount in the image creation section (drum and transfer belt) for each color, to make the relationship between the original density and the copy density become the set one. The gamma correction 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 boards and sensors include the drum potential sensor boards Y, M, C and K (DRPSB Y, M, C and K), drum potential sensor Y, M, C and K (DRPS Y, M, C and K) and the temperature/humidity sensor (TEMP/HUM). A. Explanation of the operation The gradation patch is created on the transfer belt and read by the gamma sensor (PS11). The correction value for the gamma curve is determined by the sensor output value with the predefined relationship between the sensor output and the output image. 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. • When the job starts where the process speed gets slowed down to 1/2 or 1/3 speed. However, once operated under this condition after the SW2 turns on, the operation is not carried out again until the SW2 turns off. 2-73