Image-formation system
The image-formation system, which forms a toner image on media, consists of several interdependent systems:
● Electrostatic latent-image-formation
● Developing
● Transfer
● Fuser
● Drum cleaning
The printer includes four print cartridges that contain the toner used to create the image on the media. Toner is applied in the following order, using only the colors necessary for a specific image: magenta (M), cyan (C), yellow (Y), and black (Bk).
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Figure 4-9 Image formation system
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Image-formation process
Laser printing requires the interaction of several different technologies including electronics, optics, and electrographics to provide a printed page. Each process functions independently and must be coordinated with the other processes. Image formation consists of the following five processes:
1.
Latent-image formation
2.
Developing
3.
Image transfer
4.
Fusing
5.
Transfer-belt cleaning
These processes are divided into ten steps, which are shown in
Figure 4-10 Image-formation steps on page 65 and described in the following sections.
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Figure 4-10 Image-formation steps
Latent-image formation stage
During the three steps that comprise this stage, a latent image is formed by applying a negative charge to the photosensitive drum. You cannot see this image on the drum.
Step 1: pre-exposure
The pre-exposure LED hits the photosensitive drum surface and eliminates any residual charge on the surface.
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Figure 4-11 Pre-exposure
Step 2: primary charging
A high-voltage dc bias is applied to the primary charging roller, which is made of conductive rubber and is in contact with the drum surface. As the roller moves across the drum, it applies the negative charge to that surface.
Step 3: laser-beam exposure
The laser beam scans the photosensitive drum to neutralize the negative charge on portions of the drum surface. An electrostatic latent image is formed where the negative charge was neutralized.
Figure 4-12 Laser-beam exposure
Developing stage
The developing cylinder comes in contact with the photosensitive drum and deposits toner on the electrostatic latent image.
Step 4: developing
Toner acquires a negative charge as a result of the friction from the developing cylinder rotating against the developing blade. When the negatively charged toner comes in contact with the drum, it adheres to the electrostatic latent image. When the toner is on the drum the image becomes visible.
Transfer stage
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Step 5: media feed
The printer generates electrostatic force to pull a sheet of print media to the ETB. The sheet adheres to the belt and travels between the ETB engaged motor and the attraction roller.
The attraction roller transfer positive dc bias to the media so that the negatively charged toner can be easily transferred from the drum to the sheet.
Figure 4-13 Media feed
Step 6: image transfer
The ETB carries the positively charged media over the photosensitive drum. As it passes between the transfer roller and the drum, the transfer roller applies a positive dc bias to the belt. Negatively charged media attracts negatively charged toner from the drum surface. This process is repeated for each toner color.
Figure 4-14 Image transfer
Step 7: separation from the drum
The beam strength or stiffness of media combined with the ETB holding force causes the media to separate from the drum. The sheet remains on the ETB and continues to travel through the printer.
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Figure 4-15 Separation from the drum
Step 8: separation from the ETB
The elasticity of the print media causes it to separate from the ETB. The static-charge eliminator is not involved during this step.
Fusing stage
Until the fusing stage is complete, the image is not permanently affixed to the print media. The toner can be easily smudged until the heat and pressure of the fusing process fix the image to the sheet.
Step 9: fusing
The printer uses a ceramic heater to accomplish the color-on-demand fusing process. The heater has a low heat capacity, which results in a short warm-up period and yields energy savings.
Figure 4-16 Fusing
Cleaning stage
Not all of the toner is removed from the photosensitive drum during the transfer stage. During the cleaning stage, the residual, or waste, toner is cleared from the drum surface to prepare the surface for the next latent-image formation.
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Step 10: drum cleaning
The cleaning blade scrapes the residual toner off the surface of the photosensitive drum and deposits it in the waste-toner container. The drum is now clear, and is ready for the next imageformation process.
Print cartridge
This printer has four print cartridges: magenta (M), cyan (C), yellow (Y), and black (Bk). Each cartridge holds non-magnetic, single-component toner that is composed of resins in the four colors.
In addition to the toner, each cartridge contains a developing cylinder, toner-feed roller, and stirrer.
The developer motor rotates these parts so that each print cartridge can deposit toner to form a visible image on the photosensitive drum.
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Figure 4-17 Print cartridge
The cartridges in this printer include the photosensitive drum, the primary charging roller, and the developing roller. Each cartridge performs these functions:
● Memory tag control
● Cartridge presence detection
● Developer roller engagement and disengagement control
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Print-cartridge activation
A memory tag is a nonvolatile memory that is built into the print cartridge. The DC controller reads and writes data that is stored in the memory tag. The DC controller reads data at the following times:
● When the power is turned on
● When someone closes the front cover
● When it receives a command from the formatter
The DC controller writes information at the following times:
● At a specified interval during printing
● When it receives a command from the formatter
When the read/write operation fails or the wrong data is read or written, the DC controller determines that an error has occurred and notifies the formatter of a cartridge-memory abnormality. Printing then stops.
Figure 4-18 Print-cartridge activation
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5 Removal and replacement
●
Removal and replacement strategy
●
External doors, covers, and panels
●
Internal assemblies
●
Printed circuit assemblies (PCAs)
●
Sensors
●
500-sheet feeder
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