Lexmark X 850 Owners Manual
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General information1-29 7500-XXX The Printhead also helps to clean and prepare the drum by scanning the surface of the drum at the beginning of each individual printer cycle. This action discharges a residual DC charge that may still remain on the Drum from the last print cycle. Development The toner contained within the PC Cartridge has a magnetic property that causes it to adhere to the Magnetic Roll. The Metering Blade spreads the toner into a very thin layer on the Magnetic Roll. Friction between the Magnetic Roll and the CM Blade generates a small electrical charge that is transferred to the toner. The surface of the Magnetic Roll is made up of a thin sheet of conductive material. The HVPS supplies the Magnetic Roll with two voltages; a DC voltage and an AC voltage. The DC voltage is used to transfer toner from the Magnetic Roll to the surface of the drum. The AC voltage agitates the toner on the Magnetic Roll, making toner transfer easier. The Magnetic Roll maintains a negative DC electrical potential. Negative charged areas of the drum have a lower electrical potential, or higher relative negative value than the Magnetic Roll. Discharged areas of the drum have a higher electrical potential, or lower relative negative value, than the Magnetic Roll. A discharged point on the surface of the drum now appears less negative in relation to the negative charge on the Magnetic Roll. Modulated Laser Beam 0V DRUM Drum Surface ImageDrum Surface Voltage Laser Beam Discharge Level Invisible Latent Image Laser Beam Printhead
1-30MFP Service Manual 7500-XXX The toner adhering to the Magnet Roll is always in contact with the drum surface. When a less negative point on the drum (a discharged area) comes in contact with the more negative charged toner on the Magnet Roll, toner transfers from the Magnet Roll to that point on the drum. There is now a visible toner image on the drum surface. The image is called a developed image. Magnetic RollMetering Blade TonerHVPS DRUM -VDC Drum Surface Voltage Drum Surface Image Toner at -VDC Developer Bias value Discharge Level 0VVisible Developed Image
General information1-31 7500-XXX Transfer As the paper travels between the Transfer Roll and the drum surface, the Transfer Roll applies a positive charge to the back of the printing paper. This positive charge transfers the negative charged toner image from the drum surface to the top surface of the paper. The toner image is now on the paper and the paper is now stuck to the drum surface due to the relative electrical differences between the negative electrical charge of the inner conductive layer of the drum and the positive electrical charge of the paper. Sheet of paper HVPS -VDC-VDCDRUM Transfer roll
1-32MFP Service Manual 7500-XXX Cleaning The Cleaning Blade removes any toner that remains on the drum after the transfer process. The toner that the Cleaning Blade removes is collected inside the sealed PC Cartridge and reused. Discharge At both the start and the end of each individual printer cycle, the HVPS supplies the charge roll with an AC voltage that is used to electrically clean the drum. The AC voltage removes any residual DC charge that was left from the previous print cycle. At the beginning of each individual printer cycle, the Printhead scans the surface of the drum, further discharging any residual DC charge that may be left on the drum. Cleaning BladeUsed Toner Charge roll DRUM DRUM VACVAC HVPS Charge roll GroundGround
General information1-33 7500-XXX Safety system diagram PrintheadSwitch (PC Cartridge interlock)Switch (Printer front door interlock)Switch (Printer left door interlock)Fuser cooling fan Dual drive motor ASM Transport motor Printer engine card ASM HVPS LVPS Switch(main power)Fuser unit ASM Printhead motor Printhead motor Transport motorFuser cooling fan controlPC cartridge motor PC cartridge motor Main heater lamp Sub heater lamp Sub heater lamp
1-34MFP Service Manual 7500-XXX Document scanning The document scanning section of this machine consists of a scanner that reads a single-sheet document placed on the platen glass and a document feeder that can transport a multiple-sheet document and flip the sheets for two-sided scanning. This ADF employs a constant velocity transport system that scans images by feeding the document at a constant speed over the specified position (scan position) where the carriage (full/half rate carriage) of the scanner unit assembly is fixed. Document scanning at platen Shown below is the operational overview of document scanning at the platen. ADF Scan positionPlaten registration point Full rate carriage CCD Sensor (scanner HP) Half rate carriage LensExposure lamp1st mirrorHalf rate carriage 3rd mirror 2nd mirror Rear Sensor (scanner HP) Full rate carriage Scanner drive motor assemblyCCD Image sensor
General information1-35 7500-XXX The full rate carriage and half rate carriage travel to read the document. The exposure lamp is installed on the full rate carriage. As the full rate carriage travels, the document on the platen glass is scanned and exposed with the exposure lamp. In conjunction with the full rate carriage, the half rate carriage travels half of the stroke of the full rate carriage. The optical image of the exposed document is reflected by the scanner 1st mirror of the full rate carriage and directed to the scanner lens via the scanner 2nd mirror and the scanner 3rd mirror of the half rate carriage. The image data is read with the scanner CCD image sensor assembly. Document scanning at ADF Shown below is the document feed path from the ADF. A document sheet set in the document tray assembly is fed through the ADF feed roll, ADF pick roll, and ADF registration roll assembly. The document image is scanned at the scan position, and the document sheet is ejected through the ADF feed-out roll assembly and the ADF exit roll assembly. For a duplex document sheet, the image on side 1 is scanned at the scan position and then the document sheet is inverted and fed to the ADF transport roll assembly again. Described below is the overview of the steps before document scanning and that of simplex and duplex document scanning modes. Setting a document When a document is set on the document tray assembly and the lead edge is pushed into the tray until it stops, the ADF document set actuator moves to place the sensor (ADF document set) in the unshielded (unblocked) state. Then the machine recognizes that the document has been set properly, turning on the document set LED. Preparation for feed Pressing the start button with the document set in the document tray will start feeding the document. Scan position Sensor (document tray length 2) Sensor (inverter)Inverter gate Sensor (document tray length 1) ADF feed-out roll assembly ADF registration roll assemblyAPF Feed roll Sensor (ADF document set) APF Pick roll ADF exit roll assembly Sensor (document tray length 1) Sensor (document tray length 2) Sensor (document tray length 3) Sensor (pick roll position HP) Sensor (ADF sheet through) Sensor (ADF pre-registration) Sensor (ADF APS 1) Sensor (ADF APS 2) Sensor (ADF APS 3) ADF transport roll assembly Sensor (ADF registration)
1-36MFP Service Manual 7500-XXX First the pick roll moves down and presses the document on the document tray to enable document feed. The pick roll moves down with the normal rotation of the pick roll position motor assembly and it moves up with the reverse rotation of the pick roll position motor assembly. Upon completion of document feed, the pick roll returns to the normal (raised) position. Pre-feed In the pre-feed step, a document sheet is fed from the Feed roll to the ADF transport roll assembly. To correct the skew, side1 of the document sheet is thrust against the ADF transport roll assembly rotating in the reverse direction and side2 is thrust against the ADF transport roll assembly at rest. With the pick roll at the down position (see Preparation for feed), the ADF feed motor assembly rotates in the reverse direction (CCW direction) to drive the pick roll and Feed roll. The pick roll feeds the top document sheet on the document tray toward the Feed roll. The Feed roll nipped by the separation roll feeds the document sheets (from the pick roll) one by one. When the sensor (ADF sheet through) detects a document sheet, the machine recognizes that feed of the first document sheet is complete. When the sensor (ADF pre-registration) detects a document sheet, the ADF feed motor assembly slows down. As a result, the document sheet stops against the ADF transport roll assembly, correcting the skew. Pre-registration In the pre-registration step, the document sheet (fed to the ADF transport roll assembly in the pre-feed step) is fed to the ADF registration roll assembly and then the lead edge of the document sheet is fed from the ADF registration roll assembly to the scan feed reference position (Wait Position) located upstream from the scan position, where the document stops. Thus, registration of the lead edge of the document is performed. When the document sheet is fed to the ADF transport roll assembly, the ADF feed motor assembly changes its rotational direction to the normal direction (CW direction) to drive the ADF transport roll assembly. The ADF transport roll assembly feeds the document sheet toward the ADF registration roll assembly. When the sensor (ADF pre-registration) detects the document sheet, the ADF registration motor rotates in the reverse direction (CCW direction) to drive the ADF registration roll assembly, ADF feed-out roll assembly, and ADF exit roll assembly. The ADF registration roll assembly feeds the document sheet (fed from the ADF transport roll assembly) to the scan feed reference position. When the sensor (ADF registration) detects the document sheet, the ADF feed motor assembly slows down. From this moment on, the ADF feed motor assembly and ADF registration motor decelerate continuously until the document stops in the predetermined amount of time. At this point, the document sheet stops with the lead edge nipped by the ADF registration roll assembly at 15 mm from the top. This is when the document sheet stops at the scan feed reference position. Feed roll ADF transport roll assembly
General information1-37 7500-XXX Scan control Scanning of the image illuminated with the exposure lamp of the full rate carriage is controlled by changing the feed speed according to the copy magnification. The document sheet stopping at the scan feed reference position is then fed to the scan position when the scan signal is sent from the main unit of the machine after the predetermined time lapse following the paper detection at sensor (ADF registration). Upon receipt of the scan signal, the ADF feed motor assembly rotates in the normal direction (CW direction) to drive the ADF transport roll assembly and the ADF registration motor rotates in the reverse direction (CCW direction) to drive the ADF registration roll assembly, ADF feed-out roll assembly, and ADF exit roll assembly. Each motor gradually accelerates up to the specified speed. When the document sheet passes the scan position at the specified speed, the images on the document sheets are exposed by scanning with the exposure lamp of the full rate carriage, and read by the CCD image sensor assembly. When the predetermined period of time has elapsed since the document sheet ceased to be detected by the sensor (ADF pre-registration), the ADF feed motor assembly stops. When the predetermined period of time has elapsed since the document sheet passed through the sensor (ADF inverter), the ADF registration motor stops. Inversion In the inversion step, the document sheet is inverted at the inverter gate and fed to the ADF transport roll assembly again. By thrusting the document sheet against the ADF transport roll assembly at rest, the skew of the inverted document sheet is corrected. This enables scanning of a duplex document. When the predetermined period of time has elapsed since the document sheet passed the sensor (inverter), the ADF registration motor starts rotating in the normal direction (CW direction) to drive the ADF exit roll assembly in the direction opposite to the exit direction. Thus, the document sheet is inverted and fed to the ADF transport roll assembly again. When the sensor (ADF pre-registration) detects the document sheet, the ADF registration motor decelerates until it stops. The inverter gate is so designed that the document sheet fed toward the exit can pass through it smoothly. When the trail edge of the document sheet has passed through the inverter gate, it closes the downstream document feed path. Thus the document sheet is fed over the inverter gate up to the ADF transport roll assembly when fed backward, thereby inverting the document sheet. ADF transport roll assembly ADF registration roll assembly
1-38MFP Service Manual 7500-XXX Simplex document For two simplex document sheets, feed is performed in the following sequence: 1.The first document sheet is fed to the ADF transport roll assembly. (see Pre-feed) 2.The document is fed to the ADF registration roll assembly, and then fed to the scan feed reference position. (see Pre-registration) 3.The document sheet is fed at the feed speed corresponding to the selected magnification, and the image on it is scanned with the exposure lamp at the scan position. (see Scan control) 4.As the image is scanned, the document sheet is fed and ejected by the ADF feed-out roll assembly and ADF exit roll assembly that are driven by the ADF registration motor turning in the reverse direction (CCW direction). 5.When the trail edge of the first document sheet has passed through the sensor (ADF pre-registration), the feed of the second document sheet starts. ADF exit roll assembly Document Inverter gate