Patent Application
20120177396
Reference is made to commonly-assigned copending U.S. patent application Ser. No. ______ (Attorney Docket No. 96698), filed herewith, entitled METHOD OF CONTROLLING EMISSIONS IN AN ELECTROPHOTOGRAPHIC PRINTER, by Pitas et al.; the disclosure of which is incorporated herein.
This invention relates in general to the field of electrophotography and in particular to removing waste products generated by electrophotography.
The electrophotographic process is used as a means of creating an image on paper or other suitable printing media. The electrophotographic process uses various components assembled into a print engine to enable printing. Energy consumed by the printer is converted to heat which must be eliminated from the printer to enable function.
In addition, the electrophotographic process generates contaminants which may adversely affect the printer and the external environment. Some of the byproducts of the electrophotographic process include ozone and formaldehyde and heat from the image fixing process. Other contaminants include paper dust.
Previous attempts to remove contaminants have included particulate filters, ozone filters, aldehyde filters, in combination with cooling fans, ductwork, and temperature sensors. All of these processes, while sometimes reducing the amount of contamination, have various inefficiencies. For example, a catalytic filter used for removing formaldehyde easily becomes clogged with contaminants produced by breaking down the formaldehyde. Replacement of the filter is expensive and time consuming.
A means to control heat and emissions from an electrophotographic printer while improving inefficiencies seen with other designs would be desirable.
Briefly, according to one aspect of the present invention an electrophotographic apparatus includes a photoconductor; a charging device for placing a uniform charge on the photoconductor; an image writer for writing an image on the charged photoconductor; a developer station for developing the image with toner; a transfer station for transferring the toned image to a receiver; a fixing unit for fusing the image to the receiver; and environmental control system for removing airborne contaminants from the electrophotographic apparatus.
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.
The present invention will be directed in particular to elements forming part of, or in cooperation more directly with the apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.
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Additional necessary components provided for control may be assembled around the various process elements of the respective printing modules. Meter 211 measures the uniform electrostatic charge provided by charging subsystem 210, and meter 212 measures the post-exposure surface potential within a patch area of a latent image formed from time to time in a non-image area on photoreceptor 206. Image writer 220 is used to expose photoreceptor 206 and may be a light emitting diode (LED) array or other similar mechanism. Toning unit 225, comprising elements 226 and 227 is used to develop the latent image created by image writer 220 on photoreceptor 206. Cleaning unit 230 removes residual toner from photoreceptor 206 after transfer of the image to secondary receiver 216. Other meters and components may be included.
Within the imaging module heat is generated at the image writer 220, which must be eliminated to limit thermal expansion which can cause image distortion and for stability in the electrophotographic process. Dust is generated by toning unit 225, which needs to be removed in order to prevent accumulation on surfaces which could subsequently become dislodged and spoil images.
Charging subsystem 210 creates ozone which also must be exhausted from the module. Excessive ozone levels within the electrophotographic engine may cause degradation of imaging members.
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An approach for determining airflow for cooling within office products is to make the assumption that all energy consumed is converted to heat. When energy consumed within an area of the printer is known, and acceptable temperature rise is known, airflow may be determined.
The imaging module has low energy consumption components, but is quite sensitive to temperature change. A fuser module is least sensitive to temperature change, but has high energy consumption. An electronics module can tolerate a reasonable temperature increase and has medium energy consumption. The mismatch in thermal requirements is most efficiently dealt with by the use of separate control zones using dedicated ducts and cooling fans. Using dedicated ducts and fans allows optimized filtration to address emissions particular to those produced within the zone. Dedicated air paths allow filters to be placed on or adjacent to external covers surface making for easy service.
An approach commonly used is to use a single fan with ducts tuned to provide a particular airflow to each control zone of the equipment. In practice, it is difficult to optimize the flow of each branch circuit, generally resulting in an overly large fan to compensate for inefficiency. Generally for these systems, filters are placed in ducts between the area being controlled and the fan making them difficult to service.
An alternate approach used is to use a single large fan without attempt for zone cooling. This is an extremely inefficient means of controlling temperature and contaminants. With no dedicated airflow path, the airflow must be increased to a level which would allow acceptable temperature rise for the entire machine to be limited to that of the most thermally sensitive area of the equipment. This also requires filtering the entire airstream for emissions, which leads to large expensive filters.
The optimum strategy, therefore, for temperature and emission control is the use of dedicated control zones within the printer. Once having established the optimum strategy an efficient means of controlling chemical emissions can be established.
Catalytic filters are used to decompose formaldehyde within formaldehyde laden air from the fuser process into harmless materials. Catalytic filters are also commonly used to decompose ozone within ozone laden air from charging subsystems into harmless materials. Catalytic materials are used in electrophotographic print engines so that the filter life should meet or exceed the life of the product they are used in, thus eliminating the need for service. Non-catalytic filter material may be used, however, these require frequent service thus increasing service costs. A known issue with formaldehyde catalytic filters is that they quickly lose efficiency and are rendered useless unless ozone is present as a catalytic filter renewal agent. A solution to this problem is to introduce ozone into a formaldehyde laden airstream where it might otherwise normally not be present.
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The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.
