Panasonic UF-890 Service Manual page 222

Exposure
A portion of the laser beam is deflected to the timing sensor [Beam Detection (BD) Sensor], which
controls the start timing of scanning on the OPC Drum. The CPU also uses the timing sensor to detect
abnormal signals. The light beam from the laser diode is modulated by the digital signal (nVIDEO) and
converted to parallel light waves by the collimator lens. The beam is then directed to the rotating polygon
mirror, where it is reflected to the f-θ lens and then focused onto the OPC Drum surface. The laser beam
moves across the surface of the OPC Drum in the scanning direction. Where the laser beam is applied,
the negative charge on the drum dissipates, and where the laser is not applied, the negative charge
remains. This action forms a latent, electrostatic image on the OPC Drum, corresponding to the original
image.
Development
This development process uses a conventional method, where toner coats a Development Roller and
transfers to the latent image on the OPC Drum. In the Toner Cartridge, the (mono-component) toner is
negatively charged by the friction between the rotating Development Roller (Mag Roller) and the
Developing Blade. This combination and the rotation of the Mixing Blade transfers the toner from the
reservoir and forms a brush effect on the Mag roller. Where the magnetic brush lightly touches the OPC
Drum, the negatively charged toner is attracted to the latent image on the drum, forming a mirror image
of the original on the drum. Any remaining toner is removed from the Mag Roller by the Developing
Blade and is recycled back into the toner reservoir. A bias voltage of approximately 1.7 kVACp-p at 1.7
kHz, riding on a -500 VDC bias is applied to the magnetic brush to achieve maximum print quality.
Transfer and Separation
As the paper is fed between the OPC Drum and the Bias Transfer Roller (BTR) (630), a positive charge
of approximately +600 VDC (+3 µA steady current) is applied to the backside of the paper by the BTR.
The toner particles are attracted away from the drum towards the surface of the paper. During cleaning,
the BTR is charged to approximately -800 VDC to repel toner on the OPC Drum and prevent toner from
being attracted to the BTR. After transfer has occurred, the paper passes over the Discharge Plate (617)
in the Plate Discharge Guide (616), reducing the difference of potential between the OPC Drum and the
paper. The stiffness of the paper causes the paper to separate from the drum.
Cleaning
After transfer, some toner may remain on the surface of the OPC Drum. A Cleaning Blade scrapes the
OPC Drum surface, and the removed toner is moved into the Toner Waste Box, inside the Toner
Cartridge.
Fusing
After separation, the paper passes through the Fuser Rollers and is subjected to heat and pressure in
the Fuser Unit (431). Pressure between the Fuser Roller (414) [heated internally by the Fuser Lamp
(408) to approximately 190°C (±10°C) (or 374°F)] and Pressure Roller (409) fuses or bonds the toner
into the paper.
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