Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2001-07-06
2002-09-24
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C101S181000, C399S301000
Reexamination Certificate
active
06456311
ABSTRACT:
RELATED APPLICATIONS
The present application is a U.S. national application of PCT/IL99/00668, filed Dec. 8, 1999.
FIELD OF THE INVENTION
The present invention relates in general to optical imaging on a moving surface and in particular to automatic registration adjustments of optical images on the moving surface,
BACKGROUND OF THE INVENTION
Optical imaging on a moving surface is well known, for example in laser printers and photocopiers, wherein optical information is imaged or written on the surface of a photoconductive drum. Normally, optical information is written onto the surface of a drum using stationary optics together with moving optics such as a polygon, a hologon or a galvano-mirror to axially scan the drum. U.S. Pat. Nos. 4,796,961; 4,547,038; 4,445,125 and 4,474,422, 5,315,321, which are incorporated herein by reference, describe such optical imaging systems.
When multicolor optical information is to be imaged or written, a final compound color is obtained, in general, by superimposing print separations. Each print separation has a different basic color, and the color separation prints are coordinated with and aligned relative to each other. In general a plurality of dots or patches, each of different basic colors, are printed in a same locality so as to be aligned with or superimposed on each other. Such superposition of print separations gives the impression of a full color image having colors that may be different from the basic colors.
Normally three or four separations are used, each with a basic color, (or optionally, black) in order to obtain a final compound color. In some cases additional color separations are also used. The final compound image is obtained by finely adjusting, through alignment of the system, the position of each separation, to accurately overlay the separation prints. The alignment process and the alignment itself are called registration.
When the separations are printed slightly out of registration, the appearance of an image is slightly impaired. However, if the separations are more than slightly out of registration, the effect will be disturbing to an observer. In particular, the individual edges of objects formed by each one of the separations will separate and the quality of the final multicolor image will be greatly impaired.
In order to have substantially perfect registration, the imaging system is finely tuned and adjusted prior to a printing task by performing several registration iterations until the result is judged acceptable. In practical systems, registration is usually performed by superimposing a plurality of separations of predetermined pattern(s) and visually checking the patterns for alignment. The results of the registration are only qualitative and depend on the skill of the person who visually checks the degree of coincidence of the separations and adjusts the printer.
In addition, applicants have found that for some methods of printing digital images, the apparent scale of the different color images on the final substrate may vary from separation to separation, even if they are all the same size on an image forming surface on which they are formed. This results, at best in a composite image in which at least some of the separations are misregistered over at least a portion of the image.
SUMMARY OF THE INVENTION
An object of some preferred embodiments the present invention is to provide a method and apparatus for performing image registration, preferably automatically, in an optical imaging system, for example, in a laser printing or a photocopying system.
An object of some preferred embodiments of the invention is to provide a method and apparatus for determining an amount of image scaling between the various separations, preferably automatically, for example, in a laser printing or photocopying system.
In accordance with a preferred embodiment of the present invention, at least two separations of a predetermined shape are printed in the same color to form a first pattern. This pattern is configured such that misregistration of the separations changes one or more measurable characteristics of the pattern. According to preferred embodiments of the invention, these characteristics include one or more of a print shape characteristic and an average color density of first printed pattern. The resulting print is compared to a second pattern, preferably printed together with the first pattern, whose characteristics, (e.g., shape and/or average color density) are not dependent on misregistration of the separations. The second pattern is preferably printed utilizing both separations although, in some preferred embodiments of the invention, a single separation is used to print the second pattern.
Preferably, the first pattern and the second pattern have the same average color density when the separations are registered. Preferably the average color density (or factors derived from the average color density) of the first and second patterns are compared to estimate the extent of the misregistration. In a preferred embodiment of the invention, the system registration is corrected by this estimated misregistration.
Alternatively, the first and second patterns have a characteristic distance. The characteristic distance for the first separation is not affected by misregistration of the separations and the characteristic distance for the second pattern is affected by misregistration.
In a preferred embodiment of the invention, a second print of the separations is performed with the corrected alignment and this print is checked for misregistration, which is then corrected. Preferably, additional iterations are performed until the misregistration is below a predetermined value.
After a first pair of separations is registered, one of the registered separations is preferably registered with a third separation, in the same manner as described above. Preferably, the third separation is adjusted in the registration process, so that after the second registration all three of the separations are mutually registered. This process is repeated until all of the separations used for printing are mutually registered.
In preferred embodiments of the invention, the same color is used to print all the separations, during registration, even though different colors will be used when the final image separations are printed.
A similar system is used to determine and correct for scale variations between sequential separations. One way in which such variations can occur is when the dimensions of the substrate change between sequential transfer of the separations to it. For example if the transfer process utilizes heat then the substrate dimensions will vary with successive transfers, since the substrate is heated (up to some temperature) by each of the transfers. In addition, for systems that use wet toners or inks, the wetting of the substrate may cause a change in dimension.
In order to determine scale changes a series of patterns (as described above) are printed along the length and/or along the width of the substrate. The offset of the separations is determined as a function of the length (or width) and a best fit for the function is determined. This best fit will be of the form: &dgr;(z)=a+bz. The coefficient “a” gives the required offset or misalignment correction and the factor “D” gives a scale correction which is applied to the data The scale and offset corrections can be applied to digital data, when the apparatus is a digital printer or may be applied as a magnification and offset if the data is in analog for, as in a copier.
It should be understood that the above process is most easily applied for certain system types. In one such system, a single photoreceptor is used to separately form latent electrostatic images of the various separations. The individual separations are developed using different color toners and the developed separations are transferred to substrate, either directly or via an intermediate transfer member. In many cases, the toners may be liquid toners and/or the intermediate transfer member may be heated, whic
Gila Omer
Harush Shlomo
Korol Yevgeny
Lewintz Lior
Fenster & Company Patent Attorneys Ltd.
Indigo N.V.
Pendegrass Joan
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