Electrophotography – Control of electrophotography process – Having temperature or humidity detection
Reexamination Certificate
2001-01-16
2002-05-14
Pendegrass, Joan (Department: 2852)
Electrophotography
Control of electrophotography process
Having temperature or humidity detection
C399S045000, C399S066000, C399S067000
Reexamination Certificate
active
06389241
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the fields of electrophotography and hard copy apparatus and, more specifically, to the control of printing and fixing alphanumeric text and images on print media using automatic sensing devices, feedback, and digital control techniques in a laser hard copy apparatus.
2. Description of Related Art
Basically, in electrophotography—the basic technology behind laser printing such as with Hewlett-Packard Company's HP™ LaserJet™ products—a latent image on a charged surface area of a photoconductor is developed, by application of an electroscopic toner to the area. The developed image is transferred to a hard copy medium. Both wet toner chemicals and dry toner powders are known to be used to develop an image using heat fusible toner particles. The image is then fixed, that is, fused to the print medium. (For ease of explanation, the word paper will be used as an exemplary print medium hereinafter; however, as will be recognized by a person skilled in the art, the invention described herein is applicable to all forms of hard copy media such as papers, card stock, transparencies, envelopes, and the like; the word image, or sometimes print depending on the context, is used as a generic term for all alphanumeric text, graphics, photographs, and the like; no limitation on the scope of the invention is intended nor should any be implied.)
In its basic aspects, a laser printing engine
124
, shown schematically in
FIG. 6
(Prior Art), applies a charge with a scorotron charger
136
to a moving photoconductive insulating surface area of a photoconductor, or photoreceptor,
126
. The surface area is exposed to a pattern of light
138
,
140
. A latent image of the pattern is formed on the charged surface which is then developed by application of electroscopic toner
128
,
130
,
132
,
134
(in this example, color toner) to the photoconductive material. The developed image is transferred to a hard copy medium
152
using a transfer drum
148
with a transfer corona charge unit
150
and transferred to the medium
152
by using another transfer corona unit
154
. The image bearing medium
152
is then passed to the fuser
160
subsystem where the toner is fused, or fixed. The photoconductive material insulating surface is then erased
146
, cleaned
142
,
144
, and reused for the next image. This basic construct is used in a variety of state of the art products such as computer printers and plotters, copiers and hard copy scanners, facsimile machines, multifunctional peripherals, and the like (referred to generically hereinafter as printers).
In addition to visual perception of print quality, the effectiveness or reliability of the electrophotographic process is determined in part by how well the toner image stays fixed on the media after the media exits the printing operations. Having an effective temperature in the fuser subsystem is vital to ensuring optimized image quality and achievable print. Too low of a fusing temperature can result in toner which is not properly fixed to the print media; a low strength bond between the toner and the media can cause toner to break from the media with a low degree of mechanical stress. Too high of a fusing temperature can result in melted toner adhering to the surface of the fixing device and offsetting the toner from the correct location on the print media. Either case results in undesirable print defects, often referred to as “artifacts.” Variables that determine the effectiveness of the fusing process include (1) paper parameters (the major parameters including surface roughness, thickness, moisture content, chemical composition, base weight, and size), (2) environmental parameters (the major parameters including temperature and humidity of the ambient air), and (3) fuser assembly operational parameters (the major parameters including temperature, pressure, nip size, surface properties of roller, paper speed, and fuser electrical bias).
Another factor in the determination of final print quality will be the bias voltages used in various components of the printer subsystems, e.g., the transfer voltage on the image transfer roller, the charges on various electrostatic charge/discharge elements, and the like as would be known to a person skilled in the art.
In many commercially available systems, many of these parameters are neither sensed nor controlled. The solution to their individual and possibly cumulative negative effect on print quality is to over-design the system to cover worst case scenarios. For example, a fixed fuser temperature is often used, set for a “typical media” for which the printer is compatible. However, fixed fuser temperatures cannot accommodate media types that require more heat to properly fuse the toner to the special media; fixed fuser temperatures may be too high for special media; media types requiring lower fuser temperatures may be damaged, e.g., wrinkled, by the relatively high heat of a fixed temperature fuser.
Other conventional arrangements provide user controls for manually adjusting operational parameters. Typically, such manual adjustments are made after print problems are already occurring; thus, print monitoring is required for prompt attention.
In co-pending applications, the common assignee has provided some specific, advanced solutions:
U.S. Pat. No. 6,011,939, based on Ser. No. 09/126,628, filed by co-inventor Martin on Jul. 30,1998, addresses SENSING PRINT MEDIA SIZE TO TEMPERATURE CONTROL A MULTI-HEATING ELEMENT FIXING DEVICE by relating media size to given print data;
U.S. Pat. Appl. Ser. No. 09/348,650, filed by co-inventor Martin et al., on Jul. 6,1999, addresses IMAGE FORMING DEVICES, FUSING ASSEMBLIES AND METHODS OF FORMING AN IMAGE by monitoring media qualitative characteristics to adjust fusing parameters;
U.S. Pat. Appl. Ser. No. 09/354,638, filed by co-inventor Martin et al., on Jul. 16,1999 addresses AUTOMATIC FUSER TEMPERATURE CONTROL; sensed media vibrations are related to print media type and fuser temperature selected using the measured sympathetic response;
U.S. Pat. Appl. Ser. No. 09/384,716, filed by co-inventor Martin et al., on Aug. 26,1999, addresses issues with respect to METHOD AND APPARATUS FOR DETECTING IMAGE MEDIUM SURFACE DEFECTS IN AN IMAGING SYSTEM by monitoring the fuser subsystem pressure roller and heated roller surface conditions; and
U.S. Pat. Appl. Ser. No. 09/430,356, filed by co-inventor Martin, on Oct. 28, 1999, addresses issues with respect to FIXING DEVICE CONTROL BASED UPON MEDIA TEXTURE MEASUREMENT using optical sensing; rough media requires a higher fuser temperature than smooth media.
One type of planar type fuser is shown in assignee's patent for a THERMAL TRANSFER APPARATUS FOR FUSING PRINT DYE ON A MEDIA, U.S. Pat. No. 5,541,636, file Jun. 2, 1994 by G.B. Ingram.
There is a need for an overall system approach to detecting the necessary properties of the paper and ambient environment as the paper is being processed and using feedback information to control the printing operational parameters, automatically optimizing in real-time the processes for each media type supported by the device.
SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for controlling the fuser assembly operation by substantially continuously feeding sensor information, viz., signals indicative of fuser operating parameters, ambient environment conditions, and current copy paper characteristics and performance, to a control circuit. As media is fed into the hard copy apparatus from an input supply and throughout the printing process, a variety of detection devices determine media properties, ambient environmental conditions, and current fuser assembly operating conditions such that feedback signals are sent to the controller and real time adjustments made to fuser assembly operating conditions appropriate to optimize the fixing of an image on the next sheet as it passes through. Moreover, output print characteristic detectors can be used to provide direct
Cernusak Nancy
Huffman John W.
Martin Michael J.
Hewlett--Packard Company
Pendegrass Joan
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