Electrophotographic Process
Definition
The multi-step printing process used in laser and LED printers: corona charging, laser/LED exposure, toner development, transfer, fusing, and drum cleaning; defects introduced at each stage produce periodic marks in the output.
- Steps
- Charge, expose, develop, transfer, fuse, clean
- Used by
- Laser and LED printers
- Forensic value
- Periodic marks from stage-specific defects
- Alternate name
- Xerographic process
Common questions
Why do defects in this process create marks that repeat at regular intervals on a page?+
Components such as the drum and rollers rotate at a fixed circumference, so a physical defect on one of them, like a scratch or a worn spot, contacts the page at the same interval every rotation, producing a periodic banding or spot pattern that recurs down the length of the printout.
How does a printer's electrophotographic defect pattern help link a document to a specific machine?+
The exact combination and spacing of drum, roller, and fuser defects tends to be unique to an individual unit as it wears, so matching that pattern between a questioned document and test prints from a suspect printer can support that the document came from that specific machine rather than just the same model.
Related terms
- Banding
- Horizontal density variations across a laser or inkjet printed page, arising from developer roller irregularities, drum charging variation, or drive-train gear-skip; measurable...
- Drum Period
- The repeat interval of a drum-surface defect in the printed output, equal to the drum's circumference; measured in millimetres to identify the...
- Dye-Sublimation Printer
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- Fourier Banding Analysis
- A signal-processing technique applied to high-resolution scans of laser-printed pages to extract the periodic frequency and amplitude of banding artefacts, used to...
- Machine Identification Code (MIC)
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- Piezoelectric Inkjet
- An inkjet drop-formation mechanism using a piezoelectric crystal to deform and eject a droplet without heating; used in Epson PrecisionCore and Micro...
- SEM-EDX
- Scanning electron microscopy with energy-dispersive X-ray spectroscopy. The electron beam excites characteristic X-rays from each element present in the target grain, giving...
- Thermal Direct Printer
- A printer that activates a heat-sensitive coating on specially treated paper to produce marks without ribbon, ink, or toner; used for POS...
- Thermal Inkjet (Bubble-Jet)
- An inkjet drop-formation mechanism using a resistive heating element to vaporise ink and eject a droplet; used in HP DeskJet and Canon...