HP Color LaserJet CM4730 Service Manual - Page 197
Transfer roller (Y, C, M) engagement/disengagement detection
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used for the color misregistration and image stabilization control. The pattern image for the color misregistration or image density determination is transferred onto the ETB. The ETB also controls the following: ● Transfer roller (Y, C, M) engagement/disengagement detection ● Transfer roller alienation ● ETB cleaning Transfer roller (Y, C, M) engagement/disengagement detection When the power is turned on, the DC controller applies biases to the transfers roller for yellow and black, and detects the value of current flown through the ETB according to the current return signals. The DC controller obtains information on the transfer roller (Y, M, C) engagement and disengagement. Accordingly, the DC controller executes the transfer roller engage or disengage control depending on the situation and engages the transfer rollers (Y, M, C). Transfer roller engagement/disengagement control This control disengages the transfer rollers (Y, M, C) from the photosensitive drums so that only black toner is transferred onto the ETB during monochrome printing. The ETB motor (M7) performs this control by driving the ETB alienation solenoid (SL3) while the motor is rotating according to a command from the DC controller. The following is the operational sequence of the transfer roller engagement/disengagement control. 1. The transfer roller engaging/disengaging cam inside the ETB holds up the transfer roller holder that contains the Y, M, and C transfer rollers. This brings the ETB into contact with the photosensitive drums. 2. When a monochrome print starts, the DC controller turns on the ETB alienation solenoid (SL3) to rotate the transfer roller engaging/disengaging cam. 3. The rotation of the transfer roller engaging/disengaging cam pushes the Y, M, and C transfer rollers down, disengaging the ETB from the photosensitive drums. When allowing the ETB to engage back with the photosensitive drums, the DC controller turns on the ETB alienation solenoid (SL3) again. The transfer roller engaging/disengaging cam rotates and pushes the transfer roller holder. Accordingly, the transfer rollers push the ETB into contact with the photosensitive drums. ENWW Image formation system 177
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