Patent Grant
7587163
The present embodiments relate to an electrophotographic marking system and, more specifically, to a cleaning blade useful in said system.
In marking systems such as Xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor surface. The charged 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. The latent image is developed by depositing finely divided and charged particles of toner upon the photoreceptor surface. The toner may be in dry powder form or suspended in a liquid carrier. The charged toner being electrostatically attached to the latent electrostatic image areas creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to a final support material, such as paper, and the toner image is fixed thereto to form a permanent record corresponding to the original.
In these electrostatic marking systems, a photoreceptor surface is generally arranged to move in an endless path through the various processing stations of the Xerographic process. Sometimes the photoreceptor is in the form of an endless belt and in other systems in the form of a drum. Since the photoreceptor surface is reusable when the toner image is transferred to a final support material such as paper, the surface of the photoreceptor is cleaned and prepared to be used once again in the copying process. In this endless path, several Xerographic related stations are traversed by the photoconductive belt or drum.
In these type systems, in one embodiment, after the transfer station, a photoconductor cleaning station is next. This cleaning station may comprise a first cleaning brush, a second cleaning brush and with the brushes is positioned a cleaning blade or doctor blade which is used to remove residual debris from the belt. A film or debris is generally caused by the toner being impacted onto the belt by the cleaning brushes. When the lubrication of this blade is below a necessary level, the blade can abrade or damage the belt. Toner is the primary lubricant used for the blade, however, a problem can exist with a degradation of the cleaning efficiency of the cleaning brushes or the blade. Without proper lubrication or other problems, this cleaning blade can tuck and seriously abrade the belt. Elastomeric cleaning blades, especially in doctor mode, run the risk of blade tucking. Blade tucking always starts at one of the working corners of the blade due to reduced blade stiffness at the corners and can work itself along the entire edge until the entire blade is flipped into a wiper mode-like position. Blade optimization for cleaning, filming, abrasion and other performance parameters is highly constrained by the blade tuck operating space. In other words, to ensure the blade is configured in such a way as to ensure some degree of tucking robustness, compromises must be made in the overall performance of the blade system.
The first brush above mentioned as used in prior art systems is responsible for nearly all of the filming on the photoconductive (PC) belt. This brush is positively charged to attract a negative charged toner and remove most of it from the PC belt. Adjacent to the first brush is a vacuum which vacuums the toner from the brush for later disposal. Any toner that may have acquired a positive charge will pass by the first positively charged brush and will be picked up by the second brush which is negatively charged. The vacuum is also adjacent to the second brush and should vacuum off the brush any residual positively charged toner. Then, as above noted, the doctor or cleaning blade scrapes off the belt any remaining toner debris or film layer. Again, after the action of the two prior cleaning brushes, there is generally not sufficient toner lubrication for an effective action by this cleaning blade. The cleaning blade will remove the film layer comprised of toner additives that is caused by the impact of the first brush against the toner and PC belt. The serious problem that has been encountered in this type of prior art arrangement is, as noted, that the cleaning blade does not get enough toner-provided lubrication and can easily tuck and scratch or damage the belt causing a relatively high replacement rate for both the belt and the cleaning blade. In addition, copy quality begins to deteriorate as the cleaning blade becomes tucked and is abraded and damaged or as the film and toner is less effectively removed from the PC belt by this blade. Another problem that results from blade tuck is increased drag imparted by the blade to the PC surface which can cause motion quality problems and degraded image quality.
Many of the prior art low volume electrophotographic printers and some high speed marking apparatus use elastic doctor blades to remove residual toner from drum or belt photoreceptors. Improvements in the reliability of such blades are desired to minimize/reduce wear-induced defects and extend the overall life of the cleaning blade. Unloaded polyurethane and other elastomeric materials are typically useful in cleaning blade materials. Improvements are required to extend the useful life of such blades and to make the doctor blades or cleaning blades more efficient.
The present embodiments propose in one configuration in a Xerographic cleaning station to use a corner stiffener at the ends of the elastomeric cleaning blade to prevent blade tuck at the ends of the blade. Blade tucking, as earlier noted, is a common failure mode for blade cleaners due to the low toner lubrication near the blade edge and lack of structural support of the blade edge. A variety of complicated methods could be used to reduce this problem ranging from adding extra lubrication in that region to modifying the design of the blade or blade holder. This invention in one configuration proposes to add a small stiffener to the blade ends or to the entire bottom length of the blade. By adding structural rigidity to the blade, tucking is prevented. The stiffener would be made of a rigid material. Plated steel was used for our testing but any number of suitable materials could be used (metals, plastics, etc.). The stiffener in one embodiment would be on the blade face opposite to the “working edge” (the face that contacts the photoreceptor). It is suggested that the stiffeners could be adhesively attached as a final step in the blade assembly process. Alternatively, in a second embodiment, if a molded blade was used, the stiffeners could be molded integral with the blade. When the stiffeners in this second molded embodiment are used, the stiffener could be on the face that contacts the PC (the side of the working edge) or on the opposite face or side.
While the embodiments of this invention will be described herein with reference to a cleaning blade in contact with a PC surface, the stiffened blade of this invention can be used in any portion of a Xerographic system where a doctor blade contacts a surface to be cleaned. A “doctor blade” is defined, for purposes of this invention, as a blade where the blade extension is pointing in a direction opposite to the travel of the surface being cleaned. Obviously, uses of the present invention in non-xerographic systems will occur to those skilled in the art.
In the embodiment where the stiffener is added to an existing blade, obviously, the stiffener would be on the face opposite to the face that contacts the photoreceptor (PC). The drawings and their description will further define these embodiments.
The stiffeners can be located across the entire length of the cleaning blade or can be located only in the corners of the blade depending on the specific requirements and desired conditions.
The use of a corner stiffener or a stiffener across the entire blade length have been shown to be very effective in preventing blade tuck. The stiffener consists of a plate that is adhered to the bottom cleaner blade surface on a side opposite of the working edge. The width, length and thickness and material choice of the plate may need to be optimized for the application. The function of the stiffener is to increase the rigidity of the blade corners or entire bottom edge without significantly changing the working angle or normal force at the working edge. This requires the plate to have a small width dimension. The plate should be adhered as close as possible to the corner edge though micron tolerances are not required to achieve the desired function.
The stiffener material choice is not considered critical as long as it reduces blade tuck and it is inert with respect to the materials that will come in contact with it (e.g. toner, additives, fuser oil, paper dust, etc.). If a metallic material is used as a stiffener, it may be required to be electrically grounded. The key design requirement is to achieve sufficient stiffness in the length dimension to prevent tucks. Therefore, material modulus will be important for a given set of physical dimensions. The length of the stiffener is also important as in one embodiment it should be at least as long as the blade extension length and can be as long as the entire length of the blade. In another embodiment, the stiffener can be located only in the corners of the bottom portion of the blade.
Prototypes of the cleaning blade with a stiffener have been built and tested. While exact proportions of blade dimensions to stiffener is difficult to completely describe because of the large variety of blades and their dimensions available or to be used, modeling or various empirical tests can be conducted to easily ascertain the type and size of stiffener to be used in a particular application. Therefore, while a specific numerical ratio or formula is difficult to define because of varied size cleaner blades used, tests were conducted at various stress conditions (see below) to prove reduction of tuck effectiveness for the stiffener.
In one test, the following conditions were present and prototypes have been fabricated and tested under the following stress tuck conditions:
Test Stress Conditions:
Cleaning Blade Configurations
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During the Cleaner critical parameter development phase, cleaning blade CPs such as the blade holder angle, working angle, blade penetration and blade tip distance relative to the backer roll, were optimized for cleaning, P/R abrasion and tucking. Blade tucks have always initiated near the ends of the blade 1. The tuck initiates at one end and works itself to the other end. The lower rigidity of the blade near the ends plays a large role in tuck initiation in this region. Today, there are general and loose design rules that are followed during the development of cleaning blades to prevent blade tucking. However, depending on the print engine architecture, the design rules may be very difficult to achieve. For example, extremely tight tolerances of parts may be required to hold the designed critical parameters such as blade holder angles or compensating for uncontrolled material behavior (e.g. blade relaxation). This invention provides an inexpensive and a very effective way to prevent tucking of blade 1. The cleaning blade 1 shown in
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In summary, embodiments of this invention provide a cleaning blade for use in an electrophotographic marking system. The system comprises, in an operative relationship, a cleaning blade, a holder for the blade, a movable surface to be cleaned by the cleaning blade and a reinforcement or stiffener positioned on the blade. The blade comprises on its lower portion a working edge section. The working edge section is enabled to contact the movable surface. The blade comprises an upper portion that is connected to the holder and the stiffener which is located on the lower portion of the blade is enabled to minimize the blade tucking when the working edge contacts the surface to be cleaned during a cleaning operation. This stiffener, in one embodiment, is located on lower corner sections of the blade on a blade side opposite to the working edge side of the blade. In another embodiment, the stiffener is located on a lower section of the blade across substantially the entire length of the blade and is positioned on a blade side opposite to the working edge side of the blade. In a further embodiment, the stiffener is integral with and constructed of a material substantially the same as a material in the blade and the stiffener is positioned on the blade on either the side opposite to the working edge side or alternately on the same side as the working edge side.
The blade is a doctor blade wherein an extension of the blade is pointing in a direction opposite to the travel of the surface to be cleaned. The stiffener is constructed of the same or a material different from a material in the blade. The blade, in one embodiment, is generally located in the system where it is adapted to contact and clean a movable photoconductive surface. The cleaning blade has an upper edge and a lower edge, the upper edge is connected to a blade holder and the lower edge has a stiffener attached thereto. The lower edge has a working edge which is enabled to contact and clean the photoconductive surface. The stiffener is enabled to minimize tucking of the blade when the working edge contacts the photoconductive surface during the cleaning operation. The stiffener has dimensions suitable for preventing tucking of the blade during the cleaning operation and stiffener is enabled not to adversely modify the cleaning function of the cleaning blade.
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. While for clarity, stiffeners of a rectangular cross-section are defined in this disclosure, drawings and claims, other suitable configurations other than rectangular are included within the scope of this invention. Also that 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.
| Number | Name | Date | Kind |
|---|---|---|---|
| 20040265024 | Naruse et al. | Dec 2004 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20080232874 A1 | Sep 2008 | US |
