Patent Application
20090285595
This invention relates to electrostatic marking systems and, more specifically, to a corona charging component of these systems.
When using an electrostatic marking system, a uniform electrostatic charge is placed upon a reusable photoconductive surface. The charged photoconductive surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original on the photoreceptor. The latent image is developed by depositing finely divided marking and charged particles (toner) upon the photoreceptor surface. The charged toner is electrostatically attached to the Latent electrostatic image areas to create a visible replica of the original. The toned developed image is then transferred from the photoconductor surface to a final image support material, such as paper, and the toner image is fixed thereto by heat and pressure to form a permanent copy corresponding to the original.
In a typical electrostatic system, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the Xerographic process. The photoconductive or photoreceptor surface is generally reusable whereby the toner image is transferred to the final support material, and the surface of the photoreceptor is prepared to be used once again for another reproduction of an original. In this endless path, several stations of corona charging are traversed. In known electrostatic copy processes, as those above noted, a number of electrostatic charging devices are used at various stations around the photoreceptor drum or belt. For example, at the following station: charge, recharge, pre-transfer, transfer, detack and preclean. These charging stations may involve a single corona device or multiple corona devices. Multiple corona device systems can be of a single type or a combination of different types of corona generating devices.
Many varied charging means are used for applying an electrostatic charge to the photosensitive member such as corona generating pins (Pin Corotron), corona generating wires (Corotron) or corona generating glass coated wire (Discorotron), for some examples. These devices can also be covered with a grid to further assist in generating a more uniform charge known as Pin Scorotron, Scorotron or Discorotron, respectively. These charging devices can be used as a single device or in a multiple device configuration utilizing any combination of devices mentioned. In high quality xerographic reproduction systems, a uniform charge is the foundation for production of a high quality output print.
Generally, the structure of a discorotron uses a thin, glass-coated wire mounted in an elongated U-shaped housing between two insulating anchors called “insulators”. These support the wire in the U-shaped housing in a spring tensioned manner in a singular plane. These insulators also position the wire relative to a known ground plane also known as a shield within the discorotron. The U-shaped housing can be made from aluminum and functions as the shield or can be made from plastic and is in one embodiment an elongated U-shaped structure in which case a separate shield must be provided. The corona generating electrode is typically highly conductive and when in use is placed in close approximation to the surface to be charged. Obviously, the uniform charging of a photoreceptor is necessary for the proper operation of a xerographic machine.
A by-product of corona charging devices are several gasses (most notably NOx and ozone) which are referred to in this discussion as “effluents”. Effluents must be managed in today's machines for many reasons which will be discussed in this disclosure. This management is usually through some type of air extraction and filtering system. The effluents can interact with the surrounding atmosphere, which may include organic compounds like morpholine, and with the photoreceptor itself to produce substantial negative charging effects on the photoreceptor and the resulting copy. These are sometimes called lateral charge migration (LCM) and/or parking deletion. This can cause the output of a printed copy to appear blurry or have areas where the image is entirely missing or deleted.
Nitric oxide deletions and other effluents have been a pervasive and persistent problem in these electrostatic copying systems. The shield embodiments of this invention are simple and effective ways to minimize these problems.
There are presently three forms of charging devices: corotrons, scorotrons and discorotrons. All will be referred to in this disclosure as “corotrons” or a source of “corona” discharge. The charging devices use high voltages to create a corona. This corona can be thought of as a collection of ions (charged atoms or molecules) in a local area. In most cases, the corona is influenced to move towards the desired target by the opposite charge on a screen or grid-type device.
The different names of the charge device or corotrons denote different configurations. Corotrons are simply bare wires. A high DC potential is placed on the corotron to create the corona. To charge photoreceptors to a positive voltage, a large positive DC voltage is placed on the corotron wire. To charge negatively, a negative potential is placed on the wire. Discorotrons are a wire device also. In this case, the wire is coated with a thin film of dielectric glass. Discorotrons have an alternating voltage placed on them to create both positive and negative ions. A screen or grid with a DC bias directs the discorotron's charge toward the photoreceptor. The grid voltage determines the polarity and amplitude of the charge placed on the photoreceptor.
An important consideration is that there are many ways to charge photoreceptors. Some ways have a propensity for problems to occur while others have less of an issue. In relation to nitric oxide deletions, the AC devices (discorotrons) and the negative DC devices have a higher probability of deletion problems.
The charge device is the originator of the nitric oxide parking deletion (or, for sake of clarity, deletion). The deletion process begins with the production of corona in normal atmosphere. Corona is a “cloud” of charged ions. Different types of corona contain different ions, H+ and N4+ are the major positive ions for both AC and DC devices. The negative ions NO3− and O3− (ozone) are the major ions in negative DC discharge and AC with airflow. AC devices (discorotrons) also produce the following negative ions: O−, OH−, O2−, NO2−, CO3−.
The ozone (O3) and NOx (NO and NO2) occur in relatively large amounts. These compounds are also very chemically reactive. NOx is known as Oxides of Nitrogen. While both gasses and morpholine can contribute to the deletion problem, NOx has been cited as the main culprit, hence the reference in literature and studies to “Nitric Oxide Deletion”.
Recent experiments show that the NOx output from a discorotron operated at nominal voltage is entirely NO2. Charge device NO2 output is attributed to the presence of ozone in the charge device area. Ozone oxidizes NO to NO2.
The oxidation of NO to NO2 produces one photon of light at about 1200 nm. This occurs in about 20% of the oxidized NO2. As the molecule decays to a stable state, a photon is emitted with the peak excitation of 1200 nm. This is the basis for a Chemilluenesence Nitric Oxide detector sometimes used in the prior art to measure effluents.
Photoreceptors have been shown to be very sensitive to nitric acid-type compounds (HNO3 and HNO2). The nitric acid attacks certain molecules in the transport layer of the photoreceptor rendering them too conductive. This conductivity allows any developed charge on the photoreceptor to leak to ground in the area of the attack or spread in what is sometimes (mistakenly) called lateral charge migration. Lateral charge migration is a separate issue involving the deposit of conductive salts on the photoreceptor through the interaction of corona and atmospheric contaminants, such as morpholine. In Nitric Oxide deletions, in the worst cases, areas near the acid attack appear blank on a copy because toner is not developed to the photoreceptor in those areas. In lesser extent cases, the problem manifests itself as a blurring of the image. Some volatile organic compounds, such as morpholine and organic nitrates are effluents also detrimental to the photoreceptor.
Nitric oxide deletions are often termed parking deletions. This nomenclature arises from the way in which nitric oxide deletions are most prevalent. When charging devices are run for a long period of time (during a long print run) a relatively large amount of NOx and O3 (as above indicated, collectively known as effluents) are built up. The effluents become adsorbed on the surface of nearby solids. When the machine is shut down, the photoreceptor stops rotation and becomes “parked” with a small area directly adjacent to the charge device. Over a short period of time, the adsorbed effluents are released from the charge device in a process known as out gassing. Since the photoreceptor is parked in very close proximity to the charge device, a small local area of the photoreceptor becomes damaged.
The titanium shield embodiments of the present invention provide strategies employed to combat and minimize these deletions.
It is known to use titanium to help chemically reduce effluents around a photoreceptor. (By virtue of its native oxide surface layer). It is also known to use titanium dioxide (TiO2) to remove nitric oxides from the environment via titanium dioxide coatings. See articles “Reactive Oxygen Species inhibited by Titanium Dioxide Coatings” (Suzuki et al.)) R. Suzuki, J. Muyco, J. McKitrrick, J. Frangos. J. Biomed. Mater. Res. A, 2003, Aug. 1 vol. 66 No. 2: pg. 396-402, and “Titanium Dioxide: Environmental White Knight”, L. Frazer Environmental Health Perspectives Vol. 109, No. 4, April 2001.
The embodiments of the present invention provide a novel titanium shield that fits into the housing of a discorotron. The shield has on its inboard side two raised notched ears as conductive contacts and to hold a grid in place. The shield is elongated and is coextensive with the grid and has at its bottom portion electrical contacts for connection to a high voltage source.
The discorotron that contains the shield has a typical elongated non-metallic U-shaped housing, usually plastic, with the usual wire assembly made up of a wire electrode attached at each end to anchors. The U-shaped titanium shield of the present invention fits along the length of the housing with its floor positioned below the wire assembly and its sides extending upward enclosing the wire assembly and the shield sides projecting on the inboard end beyond the sides of the discorotron housing for the purpose of mounting the grid. These projecting sides are in the form of notched ears upon which the grid is attached and secured. In an embodiment of this invention, a protective guard is placed over the upper tip of the ears to prevent the pointed ears from damaging the surface of the photoconductor when in use.
The discorotron housing has an open end at one terminal end section to provide an escape conduit for the above-discussed impurities or effluents that are formed during use and to provide means of connection to a high voltage connection. The opposite end of the discorotron housing is generally closed.
Discorotron assemblies are used to generate a more uniform electrostatic charge. To mount the grid over the high voltage wire, some inboard mounting component in the prior art would be added to the system in three or more places to hold the grid in place. Then a separate electrical contact would be added to the system to contact the grid, usually on the inboard side, thus providing some electrical potential to the grid.
The present embodiments describe a shield with an integrated grid mounting and electrical connection scheme for discorotron charge devices whose shield and grid are at the same potential. Unlike some prior art discorotrons which require three high voltage connections, the present discorotron requires just two since the grid and shield are at the same potential. The proposed integrated grid/shield assembly mates to the current high voltage connector and thereby enables the field replacement of the current discorotrons with the intended discorotrons. Advantages of the present shield include reduced production cost and improved reliability resulting from elimination of the redundant connector. The proposed shield also provides greater grid-shield and grid-wire gap consistency. A pair of stiff notched ears on the Ti shield fit into cutouts on the grid to hold the grid in place locating it the proper distance from the coronode and laterally within the device. The grid is electrified by the shield which in turn is biased from an existing connector.
This invention comprises a titanium shield with an integrated mounting feature for the grid, thus also providing the necessary electrical connection to the grid. The inboard end of the titanium shield has two extending ears that protrude slightly above the dicor housing. These two protrusions have small notches large enough to hold the grid in place. With the shield and grid both being conductive, this mounting point also provides the electrical contact. This approach is especially useful in devices where the shield and grid operate at the same electrical potential.
In
In
In
In
In
Also shown in
In summary, embodiments of the present invention provide a discorotron device comprising a non-metallic elongated U-shaped housing, a wire assembly comprising two anchors holding a wire electrode there between, a titanium shield co-extensive with the housing and fitting inside the housing, and a grid over the housing and configured to direct a charge toward a photoreceptor surface when in use.
The shield comprise at its inboard end portion thereof rising ears with notches configured to hold the grid in place. The shield also comprises on its bottom portion and below the ears at least two electrical contacts configured to provide and contact a high voltage connection to the discorotron.
In this discorotron, the ears and the electrical contacts are located at an inboard portion of the shield and the grid has apertures configured to receive and mate with the notches in the ears. The electrical contacts for the discorotron are located below the ears and form with the ears an H-like cross-sectional configuration when viewed from an end view. The wire assembly of the discorotron is located between the grid and a floor of the shield. The ears extend upwardly beyond side portions of the housing and are configured to leave space to receive and hold the grid in place.
A guard is positioned over projecting end portions of the ears. This guard is enabled to avoid damaging contact of the ears and a photoreceptor surface when in use.
The discorotron has in an inboard end portion thereof an open section to provide for escape of effluents and in an air block on an outboard end to prevent discorotron air leaks and provide structures to position a discorotron removal tool.
This novel shield has a grid over its upper surface and comprises an elongated shield structure of titanium having a U-shaped cross-sectional configuration with two upstanding sides. The shield is co-extensive with the grid and configured to fit into a housing for the discorotron. The shield has an open end in its upper section. The shield has on its inboard upstanding side end portion thereof a pair of projecting notched ears. These ears are configured to protrude above and beyond the upstanding sides. The ears are adapted to provide connections to the grid and to hold the grid in place. Positioned below the ears are electrical contacts to a voltage source.
It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
