Typewriting machines – Sheet or web – For feeding plural record media concurrently or selectively
Reexamination Certificate
1999-09-29
2001-02-27
Eickholt, Eugene (Department: 2854)
Typewriting machines
Sheet or web
For feeding plural record media concurrently or selectively
C400S703000, C271S258010, C271S258040
Reexamination Certificate
active
06193426
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to printing devices and, more particularly, to the need to change feed rollers on such devices as the rollers wear and/or become contaminated with particles from abraded media.
BACKGROUND OF THE INVENTION
In the realm of peripheral equipment for data processing systems, it is difficult to think of a device that is more reliable than a modern laser or ink-jet printer. In spite of their inherent reliability, such printers do require rather infrequent periodic maintenance. One of the items that is subject to degradation with use is the media feed, or pick, roller that is responsible for grabbing a single sheet of print media from a paper storage tray or bin and feeding the sheet into a series of transport rollers which direct the sheet along a path within the printer. Various types of print media, such as bond paper, cotton-fiber bond paper, recycled paper and plastic transparencies, may be used, depending on the type of printer. Typically the media feed roller is either cylindrical or a section of a cylinder (i.e., pie-shaped when a cross section is taken perpendicular to the cylindrical axis). As a general rule, media feed rollers have a resilient rubber outer coating, layer or sleeve that has a high coefficient of friction. There are three main reasons why feed rollers must be periodically replaced. Firstly, with use, the outer surface of the roller gradually wears, thereby reducing its radius. As the radius decreases, the area of the roller which contacts the upper most sheet of a stack of print media sheets under an applied pressure during a media feed operation also decreases. As the area of contact decreases, so does the ability to reliably pick up individual print media sheets. Secondly, normal aging of the rubber compound by, for example, exposure to ozone in the atmosphere, can reduce the coefficient of friction. Thirdly, the media feed roller typically becomes contaminated with abraded media particles. Paper, the most common print medium, contains a potpourri of ingredients, which may include cellulose fibers; rosin (added as size to decrease the rate at which cellulose fibers absorb water); fillers such as clay, titanium dioxide, talc, and calcium carbonate (found chiefly in recycled paper from Europe); and various dyes. As paper is abraded by the feed roller, a some of the resulting cellulose and filler particles (e.g., clay, titanium dioxide) become embedded in the surface of the roller. Other abraded particles (most notably the abietic acid molecules from the rosin and the various organic molecules from which the dyes are formed) become dissolved within the rubber itself. Once dissolved, they freely migrate within the rubber, thereby changing the chemical and mechanical characteristics of the rubber. Contamination of the rubber on the media feed roller invariably reduces the coefficient of friction, making paper feed failures increasingly likely. Feed failures may be take several forms which may include: a complete failure to feed the media sheet, a late feed of the sheet, or a jam related to differential feed rates from one side of the sheet to the other. Collectively, these media feed failures will be referred to as misfeeds. Though the roller may be cleaned with an organic solvent such as alcohol, its coefficient of friction is unlikely to be restored to original specifications. Of course, contaminants dissolved within the rubber cannot be removed by a simple cleaning. At some point, the media feed roller must be replaced in order to minimize media misfeeds and restore printer performance.
The misfeed rate caused by media feed roller malfunction follows an interesting pattern. For a high-end printer with a new media feed roller, the feed failure rate will be around 1 misfeed per 10,000 pages, with replacement of the roller being made when the failure rate is greater than about 1 misfeed per 500 pages. Using print media of low abrasiveness and low pollutant content, this excessive jam rate will begin to occur when the roller has fed about 350,000. For a new low-end printer, a somewhat higher feed roller related feed failure rate of about 1 misfeed per 3,000 pages is considered acceptable, and replacement is usually made when the failure rate is greater than about 1 misfeed per 100 pages. With ideal use, the unacceptably-high misfeed rate will be reached when the roller has fed about 100,000 pages.
What is needed is a method for alerting the user or a network administrator of the need to replace a media feed roller. In most instances, it is not enough to simply alert the user after a total number of pages have been printed which correspond to the expected life of the roller under ideal service conditions. Due to greatly varied printing conditions, the roller may require replacement sooner.
SUMMARY OF THE INVENTION
This invention provides a method for determining the optimum time for replacing a media feed roller in a printing device, such as a printer used in connection with a data processing system, or a stand-alone copier. It has been ascertained that the misfeed rate associated with media feed roller failure follows a characteristic pattern, which may be treated as a step function. That is to say that, beginning with a new media feed roller, the feed failure rate, which is usually measured in pages printed between misfeeds, remains relatively constant. However, as the time for replacement nears, the graph begins to plunge precipitously, as misfeeds begin to occur with increasing regularity. After the plunge, the misfeed rate continues to increase, but at a decreasing rate. Eventually, the feed failure rate reaches a value that represents a misfeed during every page feed. Like most natural processes, there is a normal variation in feed failure rate. In addition, the curve may be linearly compressed by utilizing highly abrasive print media or print media high in contaminants, or linearly expanded by utilizing print media low in contaminants and low in abrasiveness. The optimum time for replacement is deemed to be shortly after the graph begins to plunge. However, because there is a certain degree of randomness to the feed failure phenomenon, it is necessary that notification of the need for replacement of the media feed roller be given based on accumulated data sufficient to make a statistically valid directive to the printer user, rather than making a directive based simply on one or a few data points that may be at the extremes of a normal distribution and, therefore, not representative of the true state of the media feed roller. The simplest and most reasonable technique for providing a roller replacement directive to the user is to begin tracking feed failures when a feed failure rate value falls within a predetermined replacement range for the first time. After a statistically significant number of subsequent misfeeds indicate that the misfeed rate average is within the fixed replacement range, the replacement directive may be issued. The message may take one or more of several forms, such as a synthesized voice warning, a warning message appearing on a digital readout, the turning on of a warning light, or the sounding of a buzzer. If the printer is installed on a network, notification may be sent to the user performing the printout, to the network server console, or to both locations. Another, more complex, method of determining the optimum time for roller replacement assumes that the misfeed rate is a function of the total number of pages printed. Thus, non-linear regression analysis may be performed on data points already recorded in order to extrapolate the expected shape of a future portion of the misfeed rate curve. Though the basic shape of the misfeed rate curve may be determined experimentally for each media feed roller type, the curve for use in the real world will vary for each printing device. The amount of variance from the experimentally determined curve will depend on the actual conditions of use (e.g., the mix of paper chemical composition and abrasiveness over the life of the roller). By tracki
Eickholt Eugene
Hewlett--Packard Company
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