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File name:Photocopying Processes.pdf
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Descr:Photocopying Processes
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File name Photocopying Processes.pdf

Photocopying Processes Overview Overview Charge Exposure Development Transfer and Separation Cleaning Quenching Fusing 1 1. Scanning An exposure lamp illuminates the original. Light reflected off the original is used to create the image on a drum*. In analog machines, the light is reflected through a series of mirrors, eventually striking the drum directly. For multi-copy runs, the original must be scanned for each copy. In digital machines, the reflected light is passed to a CCD or CIS, where it is converted into an analog data signal. This data is further converted to a digital signal, processed, and stored in memory. To print, the data is retrieved and sent to a laser diode. For multi-copy runs, the original is scanned only once and stored to a hard disk. * In this overview section we refer to the photoconductor as a drum just for simplicity. However, be aware that the photoconductor is often an OPC belt rather than a drum. 1 April 2001 Page 90 Photocopying Processes Overview 2. Charging A charge is applied to the photoconductor drum. There are a variety of methods for this. Some machines apply a positive charge, others apply a negative. Most use a non-contact corona wire--though some use a contact, charge roller. The drum holds the charge because the photoconductive surface of the drum has a high electrical resistance­unless exposed to light. 2 8 3 7 4 6 3. Exposure 5 In an analog machine, the light reflected off the original is redirected to the drum. In a digital machine, the processed data from the scanned original is retrieved from memory or from a hard disk and transferred to the drum by one or more laser beams. In both cases, the areas exposed to light lose some or all of their charge. This writes an electrostatic image on the drum. 1 April 2001 Page 91 Photocopying Processes Overview 4. Development Toner is attracted to the latent image on the drum. The exact process varies depending on whether the drum holds a positive or negative charge. Most analog machines are Write to White--the toner is attracted to unexposed areas on the drum. Most digital machines are Write to Black--the toner is attracted to exposed areas. 5. Transfer The image is transferred to paper. Some machines transfer the image directly from the drum. Others use an intermediary transfer belt. Transfer belts are particularly common in color machines. The four colors are layered onto the belt, and then the final image is transferred to the paper in one step. 6. Separation The paper can be separated from the drum (or image transfer belt) electrostatically or mechanically. Charge coronas, discharge plates, pick-off pawls and sharply curved paper paths are all used. Often a machine will combine two or more methods. 7. Cleaning The remaining toner is cleaned off the drum. Most machines use a cleaning blade to wipe off the excess toner. Some add a cleaning brush or cleaning roller to improve efficiency. 8. Quenching Light from a lamp neutralizes the remaining cha

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