Typewriting machines – Typing by other than type-face or type-die – Thermal
Reexamination Certificate
2001-06-28
2002-05-21
Hirshfeld, Andrew H. (Department: 2854)
Typewriting machines
Typing by other than type-face or type-die
Thermal
C400S118200
Reexamination Certificate
active
06390696
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to printers having fuser units that fuse toner, ink or other printing compositions to a sheet of print media such as a sheet of paper. More particularly, this invention relates to systems for improving the print quality of such printers by adjustment of the operating temperature of their fuser units.
2. Prior Art
It is well known that changes in the operating temperature of a printer's fuser unit can effect the quality of that printer's work product. For example, one print quality problem arises from the fact that printers in general, and their fuser units in particular, heat up during extended periods of use. These increasing temperatures can cause changes to those conditions under which a toner or ink best fuses to successive sheets of print media. Thus, increasing fuser temperatures can cause undesired changes in the overall quality of a printing task—and especially those printing tasks involving a large number of successively printed sheets.
Another print quality problem arises out of the fact that these fusing operations tend to shrink successive sheets of print media, to increasing degrees, as the fuser's operating temperature rises. In the case of paper print media, these fuser induced sheet size variations are related to the moisture content of successive sheets of paper undergoing printing. For example, it is well known that a sheet of standard 8½×11 inch bond paper can shrink as much as an eighth of an inch in either dimension as a result of going through a printer's fuser unit. A sheet of paper that has absorbed a great deal of the liquid component of an ink, or of a liquid toner, may shrink even more (e.g., up to a quarter of an inch). Those skilled in this art also will appreciate that paper shrinkage in the cross grain direction (normally the width of a sheet of paper) is usually greater than shrinkage in the grain direction (normally the length of a sheet of paper).
Such changes in paper size are generally regarded as being undesirable. They can be especially undesirable in duplex printing operations where a sheet of paper receives printed information within a bordered region on a first side and then undergoes a fusing operation in order to fuse that printed information to that first side. This fusing operation causes the paper to shrink. In a duplex printing operation, that shrunken sheet then undergoes printing on its second side. The information printed on the second side is sized (e.g., in a computer file) in the “expectation” that the print media upon which it is to be placed will be the same size (e.g., 8½×11 inches) as the sheet which received the first printing. This expectation may not be met. For example, an original 8½×11 inch sheet of paper may have shrunk as much as the previously noted quarter inch in each direction as a result of the fusing operation. In this circumstance, information printed on the second side of the sheet may appear to be larger because the sheet upon which it is printed is, in fact, smaller. Consequently, information appearing on the second side of some kinds of paper also will tend to “show through” the paper in the border regions of the printing on the first side of that sheet of paper. This condition can create visual effects in the border regions of the first side that vary from reader annoyance, to unprofessional appearance, to commercial unacceptability.
In order to accomplish the toner transfer part of such processes, a sheet of paper must pass between a transfer roller and a photoconductor drum. During the toner transfer, the transfer roller electromagnetically attracts toner particles away from the surface of the photoconductor drum and onto the surface of the sheet of paper. The electrical resistivity of the paper is one of the many factors involved in this toner transfer from the drum to the paper. This electrical resistivity is especially effected by the moisture content of the paper receiving the toner image. This moisture content is, in turn, effected by an electrophotographic printer's fuser temperature. Thus, in a duplex printing operation carried out by an electrophotographic printer, a fuser temperature change will cause a paper moisture change, which will cause a toner transfer change, which in turn will cause a print quality change.
Those skilled in this art also will appreciate that some printers have dealt with some fuser temperature related problems by allowing manual selection of a fuser temperature. Such selections are usually based upon the nature of the print media to be employed. For example, user selection of a heavy paper print media may call for the printer's use of a higher fuser temperature mode of operation. This higher temperature provides better print composition adhesion by producing the increased thermal mass transfer needed to sustain adequate fixing of a toner or ink to a heavier grade of paper. In making this selection, a human operator must first recognize that a heavy paper has been selected. That human must then push an appropriate button on the printer's control panel. If use of the heavier paper is not recognized, or its need for an increased fuser temperature not appreciated, or if the wrong control panel button is pushed, the quality of the printing may suffer.
Another example of a need for selection of a different fuser temperature operating mode might involve printing upon transparent print media since such media are usually best employed using relatively lower fuser temperatures. Such lower temperatures are needed in order to prevent melting or other deformation of the transparent print media itself. Here again, the user must realize that the transparent print media selected requires a lower fuser temperature, and then press the correct button on the printer's control panel to get that lower temperature.
Thus, under current practices, change of a printer's fuser temperature requires user recognition of a potential problem arising from the nature of the print media and a correct manual intervention via a front panel interface. Unfortunately, the need for even these relatively simple temperature changes are not intuitive in nature to most users. Moreover, user education is not always an effective way of dealing with this problem since many users do not read the printer's operating manual, or are otherwise unaware of the print quality problems that can be caused by selection of inappropriate fusing temperatures. Even fewer users are aware that a fuser's temperature may vary during extended printing operations and/or that these temperature variations can effect the quality of an overall printing task. Thus, many users often interpret poor fusing as a product quality issue. This can result in unneeded service calls—or unjustified user dissatisfaction.
SUMMARY OF THE INVENTION
Applicant addresses the previously noted fuser temperature change problems and/or mistaken manual selections at a printer's control panel by providing those printers that employ fuser units (e.g., electrophotographic printers, inkjet printers and so on) with a fuser temperature control system that automatically changes a fuser's operating temperature when such a change is needed. Hence, use of printers provided with the hereindescribed self-adjusting fuser temperatures minimize, or entirely eliminate, the need for user knowledge and/or user interaction with a printer's control panel.
In its broadest sense, the automatic fuser temperature changing printers of this patent disclosure are comprised of (1) a printer, (2) at least two temperature sensors and (3) a printer microprocessor component or separate computer that compares two sensed temperatures and sends signals to a fuser having two or more temperature modes. Applicant's automatic fuser temperature selection is preferably carried out by (1) a first temperature sensor in a first zone of the printer, (2) a second sensor in a second zone of the printer a
Hirshfeld Andrew H.
Nolan, Jr. Charles H.
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